Newbie questions

[JONYARIAS]

I recently decided to get into metal detecting and went ahead and purchased a used CTX-3030. My wife is from a small ranch south of Chihuahua city with no cell service. We go 3-4 times a year for 5-10 days at a time, so I figured this would be healthier than driving around in my side by side drinking beer all day. Like every remote small remote community in Mexico, there's treasure in the mountains, supposedly. This is my first metal detector and it was my first time actually assembling it. Every thing worked fine and I took some old Mexican coins (1892 8 Reales, 1908 libertad, and a 1972 Benito Juarez) from my collection to test the CTX3030. I would get a 1-43 to 1-46 reading from these coins when I ran the CTX over them on the surface. I put the coins behind an old adobe wall thats about 5 inches thick, but the metal detector would pick them up in the coin settings. I had to turn the sensitivity almost al the way up. Is that normal for silver coins? The other problem I had was that almost everywhere I tested also gave me a reading of 1-46 @ 12 inches. I dug and dug and it would continue to read the same depth. I am completely new to this, so any input is welcome. I did find an old horse, bullet shells, and an old horse shoe nail at about 12" deep under a lone white oak tree on a mountain side about 45 minutes hike from the last rode my sided by side could make it to.