I've found good skin stretching is more important for ATG than WTG or XTG.

Another thing I found to help is that when I do my XTG pass, I do a few buffing strokes and with each stroke adjust the angle to go more atg. So by the end of my XTG, I've actually shaved at about a 45 degree angle ATG.

Restropping before ATG also helps a lot. The blade needs to be at its sharpest for ATG, and is fairly blunted after WTG and XTG.

Lastly, I lay the razor almost flat on my face for ATG.