I use whichever W/H gives me results I want. Usually 16x on each sometimes down to 4 (H).
If its non-anamorphic and you have to crop the sides, then 720w is too much. If you cut 8 from each side (total 16), then 704w is right without zoom. Height is always subjective, so I get the horizontal correct first, then use the a/r readings to guage the proper height.
I know some (many) might disagree, but If you have trouble with AR, sometimes leaving a small ugly black bar on top or bottom fixes it to display correctly. For example you cropped the black off of the top bottom, but are getting a 0.1% error, leave some black and it might go to 0.0%. Thats only for 32x divisible resolution, for compatibility.
Since I have abandoned caring about shitty standalones, I haven't had to do that.