It’s normal to not to be able to get right into the corners because windows sees the guns as analog controllers, which have a circular range of motion, but you should be able to get very close to the corners to a point where it won’t make much of a difference.
The jumping can be nullified in the calibration. Have a look at the image attached. I had a similar image set as my wallpaper for calibration in windows. This image is an example of if the crosshair jumps when it gets to the right hand side of the screen. The black square is the screen, the blue square is the aim movement of the guns of which to follow during calibration. Follow this blue square 5 times or more in the 1st calibration screen but when getting to the corners follow the red arrows a few times to get into the corners. The blue cross shows centre of shot for 2nd calibration screen. If the crosshair jumps at other sides of the screen instead, rotate image to suit.
Regarding MAME, make sure your MAME resolution is the same as your windows resolution or calibration will be off in games. Also, adjust MAME.ini settings as per in the original thread.
Lethal enforcers doesn’t have a calibration menu but has a shot test screen where you can shoot each square on the screen to see how close your windows calibration is.