The huge amount of flat surface area on the front and back of a coin VS. relatively none on the edges means that they are nearly ......always .......going to be flat and not on edge , just simple physics. On edge coins do happen from time to time but are much more rare than people think , so rare that I dont even consider them or have any concern over how a detector reads them.
I read many posts on the internet forums where people are describing a coin they found on edge , I call B.S. on most of them , .....unless you get very .....very lucky and somehow manage to not disturb that coin in the soil its in as you are digging it , which itself might be a one in a million shot , there is no way you could possibly know that coin was on edge. Coins carefully pulled from an intact flipped plug could be identified correctly as on edge at times , so I will give you that ,.....but under any other circumstances you are nearly always going to dislodge any target you are digging and disturb the soil its sitting in long before you can identify whether it was on edge or not.
Ive been detecting over 20 years , found thousands of coins , and really cant tell how many if any at all were on edge. It really is that unlikely that anyone else could either. Usually its something people " assume " because the signal sounded weak or only hit one way , which is better explained as partial masking than an on edge coin........