I'm not sure you mean -- where did you get that information about
fractional versus integer ratios? Isn't pretty much all Chinese text
fixed-width (monospaced), i.e., all hanzi are the same width? The only
variation is in how different fonts handle standard Latin text and
punctuation (including space characters). Most are variable-width
(proportional) for that. Of course, you can use full-width Chinese-
style punctuation instead, but that has a distinct look.
Anyhow, for Latin text and punctuation, the only monospaced Chinese
fonts that I'm aware of are NSimSun (as opposed to the proportional
SimSun) and MingLiU (as opposed to the proportional PMIngLiU), which
come with Windows. I'd try them. NSimSun might be a better choice.
MingLiU has some issues in Mac OS X that might or might not be a
problem, so it's best avoided if you can do so. See here:
http://www.yale.edu/chinesemac/pages/fonts.html#Microsoft
If you're in 10.5 or later you'll have no trouble with these. I'm sure
there are others, but I don't know which.