Yep, mine seems to be pretty hot no matter what coil I use. "I have all three".
The only thing I've noticed is a change in depth reading. And that's to be expected
when you think about it. The machine doesn't recalibrate for coil changes.
I've never tried accurately measuring the depth read differences between the various
coils, but as a rule, if you are using the sniper coil, you can divide in half what the
depth reading says. IE: if it says four inches, it's probably closer to two.
With the 9x12 coil, again I haven't really tested it, but I would expect a slight
change from the stock coil. IE: if it reads four inches, it might actually be five
or six. The change should be in proportion to the change in coil size.
But as far as sensitivity, I've never noticed in real issues changing coils.
That will more pertain to the coil being correctly tuned for the frequency rather than size.
In fact, my sniper coil is HOT for it's size. No problem there at all.
And the 9x12 seems fine also. The only thing I notice about the 9x12 coil is
that to get the very most depth performance, you need to run the machine as
hot as you can stand it. There is quite a noticeable difference in total depth
performance between say running half way, vs nearly full blast.
But of course, this will only matter if you are seeking targets that are actually
that deep. Many targets are not that deep, so much less an issue.
I run the sniper full blast most of the time with little falsing.
Heck, I run all my coils as hot as I can stand em..