That lawn looks VERY pretty, Very flat, and well manicured. How long have you lived there and did you or the prior owners haul in "new" dirt for the lawn?
1/2 of my mother's lawn was dug down 6" and new sod was brought in when I was a kid. I find all sorts of cool things on the WEST side of the yard, and only clad and new stuff on the east side.
one thing I have learned is that you can't judge a yard by the house, some of the nicest, oldest houses had very little in the yard, and some of the smallest crummiest houses had the most goodies, you never know!!!
As BigAl suggests, you can try "planting" various items and then see how your detector reads/sounds with various settings. Learning your machine will be much more rewarding in the long run as opposed todown-scaling for a cheaper, less sensitive machine. Pay your dues and read and practice.
I have the same problem here. House was built in 1987 and it was pastures & woods before that. I have found three coins on my 20 acres - all clad. Some interesting relics, though. 1947 Dog tag, tractor parts, snapped soil implements, dozens of bullets, yards of chain and miles of barbed wire.