That is a good question, and I agree that there is likely some room for improvement in terms of accuracy.
I do not use DJI apps to determine FLY/No Fly areas. First, I check the sectional, then confirm using Airmap, and then again using a spot location taken using the AirMap app. When I relate the Airmap map to the actual terrain features on the ground, it appears as though I am just outside the FRZ.
On the actual sectional chart (SkyVector), the recorded lat/long using the AirMap app is within one minute of the coordinates on Skyvector for the same map spot (as as close I I can eyeball it).
It would probably make sense to record the spot location again using another GPS device. If the area I am interested in is indeed permissible WRT the the FRZ, it is so only by a few hundred feet. The ink lines on the sectional are that wide. ?
I have attached a screen shot of the location I am researching FYI.