Ok,a few things will dictate results and they are, in order of importance...LOCATION,EQUIPMENT/OPERATOR,PERSEVERANCE. I don't know your level of experience so I'll assume you at least have been detecting SOME before. I will also say the Explorer SE is different in some ways than the Explorer2,which is what I have. I'll go so far as to assume the models are similar enough that you can run yours like mine and have similar results.
I've done quite well with the Explorer2,once you have a couple hundred hours of detecting time in you'll know what to do and what not to do,and what you CANNOT do,depending on the site you are in.
If I am in a site with little to no EMI,I will run Manual Sensitivity up until it's starts making erratic noises WHILE THE COIL IS SITTING STILL,and then turn it back down 2-3 points. Be sure to have your Threshold just barely humming so you can hear it,and it must remain humming WITHOUT ANY erratic noises for 10 seconds straight. That way I know the machine is stable,and for ME,the machine HAS to be stable. If you have EMI,the machine is interpreting that noise as actual signals,and you will not be able to tell a good faint deep target from an EMI false,you will chase your tail all day. Again,I'm assuming you don't have a lot of time with this machine,or any machine for that matter. The Explorers CAN be run at full Sensitivity and making all kinds of noise,but that is not for this discussion. If you're asking MY advice,you are not anywhere near running an Explorer full tilt. No worries,neither am I.
The coil/machine combo I LIKE the most and the combo I USE the most are different. I'll keep this conversation geared toward a larger coil. You are going to run the Ultimate 13",while I have a 12.5" Sunray X-12. The X-12 is the coil I use the most,because it is STABLE,gets very good depth even while running in Auto,and it is ACCURATE with tonal response,ID and separation.
This is how I run it,everywhere I go,with tiny tweaks as needed.
Tone section-
Threshold 5 (Be aware that changing the Threshold tone shifts the ENTIRE range of tones for targets,you'll see what I mean if you dont already know)
Variability 10 (This allows for the greatest difference between tones-very handy)
Limits 10 (This allows the machine to use its entire tonal range,just use it)
Volume section-
Max Limits 10 (Allows for full volume output,adjust the volume in your headphones as needed)
Gain 10 (Any target the machine sees that is not discriminated out will have the same or very similar volume)
Sounds section-
Ferrous (If you choose to run Ferrous,the machine will give you an audio response according to how Ferrous the item is. Be aware that if either in Ferrous or Conductive,the cursor placement and VDI remain UNCHANGED,only the tones you hear are different.)
Options section-
Response Normal (The other options just sound like crap to me)
Recover Fast and Deep are usually both OFF. If I'm having trouble in a lot of trash I may turn Fast ON,which allows the Recovery to be sped up to some degree,I usually notice that the signals are less robust and kind of "thin" when using this. It is a last resort when combatting trash with the large coil. I may turn Deep On when I'm in a field or a somewhat less trashy park and I'm having NO luck,just to try and reach a bit further. This is a SLOW SWING application,you're going for the deepest of the deep. Don't get caught swinging TOO slow,you'll miss stuff that way too,usually a 3-4 second sweep of 4-5 feet is what I use. You can certainly go slower than that,but it has to be fast enough to outrun the Autotune of the machine or it will interpret a super deep faint target as just more of the ground.)
Noise I always let it Noise Cancel by itself,automatically,before every hunt and again every 15-30 minutes,depending on how far I've travelled from my starting point. It may not be needed but if it was and you didn't do it,you could be sacrificing performance. Remember,in MY world,were looking for a stable machine,or as stable as we can get it,right at the edge of instability and then down a point or two. If you Noise Cancel at Manual 20 and you still get a bit of erratic behavior while the coil is motionless,turn it down to 19,18,17....you get the picture.
That's about it for settings. I run NO discrimination and listen for solid/fairly solid REPEATABLE high tones when coin hunting,which is all I do. I look for numbers with FE reading of less than 20 and CO readings of more than 22-23. Keep in mind this is DEEP coin hunting,6" and deeper. Coins shallower than that usually have better readings,lower FE readings and higher CO readings. CO numbers of 30-31 are generally hot rocks or junk of some kind,but multiple coins together can push funny numbers. If it sounds weird in all aspects you might want to check it out with the shovel...but if there's a certain amount of goodness to the signal and it's got that depth meter about empty,it should be investigated!
Lastly....Manual Sensitivity will get more depth in just about EVERY situation when used according to the above setup. It HAS to be stable. You will be very pleasantly surprised at how deep that Ultimate will find coins at silly depths with Manual Sensitivity used in moderation. High Manual Sensitivity will pick up on ANYTHING within the detection field of the coil,including the smallest flake of iron,minerals,etc and will WREAK HAVOC on your brain. DONT DO IT! Auto Sensitivity is great for that "Sunday drive" around the park when you just don't want to think about setups too much and you don't want any trouble. It'll cost you a couple of inches in depth but it's nice to use sometimes. Auto CAN and WILL go deep,but the ground conditions have to be very favorable,with the right moisture content,low minerals,light trash,etc. I have found MANY more DEEPER coins running Manual Sensitivity 18-22 than I have running ANY other way.
Use this advice at your own risk Grasshopper. It's what I do. As Bryce said,there really isn't any right or wrong,but there ARE certain setups that will optimize your coin hunting. The biggest difference with MY setup is running Ferrous ALL the time...EVERYWHERE. Once you run your SE for awhile you'll become acutely aware of why you should do something and why you shouldn't,according to where you are.
I'm tired,it's late,good night.
