Thank you for the detailed comment.
This program uses brightness equalization of different parts of the original image, otherwise dark and light areas will not fit well. This alignment has a radius (the same one), if it is greatly reduced, the image becomes flatter.
At the expense of cutting off excess areas is a good idea, it remains to figure out how to make it as simple as possible for the user, I do not turn the program into a new Photoshop.
On the Mac, the program should work under Wine (I have no way to check) if you add there msvbvm60.dll : https://disk.yandex.ru/d/-HtgaMCt3MvXQo