Once again, there is far more junk than treaure out there and some excellent treasures can masquerade as junk. For example, a 5$ gold piece can appear like a bottlecap to your detector. You are fortunate in that you have intimate knowledge of your current hunt site, an old mid-1800's property (which ties directly into my "Know Before You Go" advice).
There is a possibility of finding one of these VERY desirable gold coins there. Remote, I admit, but the chance exists. Would you wanna miss it, simply because your detector said it was junk instead of treasure - and you believed it? Other things from buttons to cow bells can read as junk, too. The moral of the story here is:
DONT rely on your machine to tell you the difference.
Instead, dig more than watching that meter. While I know what the ad hype says about your detector, the TID is only an indication of likely conductivity, and should be considered as nothing more than that. If you have doubts of this, as well you might, consider the goodies that Les The Bluenose unearths - he uses an old Garrett Freedom III, which has no TID features. All he has to go on is the audio and a little knob twiddling to "sorta" tell him what it might be. As a consequence, he digs a lot. My personal inner dialogue goes like this: "Hmmmm, the TID says it's a pulltab (bottlecap, foil, etc.) - let's see if it's right."
Here's an old trick, Judy, to help hone your instincts. You may not like it, after youve spent $$$USD on an ID instrument, but it's good practice. Get some black electrical tape and cover the ID blocks on your Ace 250. Then, use only the cleanliness of the audio and your PP indications in deciding to dig.