I always question and I have a problem with any track 'standard' that does not include tolerances for complex trackwork. According to my figures and observations you need to work to with an accuracy of around +/-0.025mm if you want to have complex trackwork with crossing K's using the 31.5mm minimum track gauge, 1.5mm flangeway combination.
The prototype does not use +/- tolerances. Track dimensions are Max or Min.
Track Gauge is 31.5mm MIN. It can be more, and often is on sharp curves.
Check Gauge is 30.0mm MIN. It can be more.
Crossing Flangeway is 1.5mm MAX. It can be less.
However, the scope for variation of the last two is limited because the Check Span is 28.6mm MAX.
i.e. you can reduce the flangeway by 0.1mm, or increase the check gauge by 0.1mm, but not both by the full amount at once.
It's impossible to say that you have to work to this or that accuracy, because we don't know the wheel profile or back-to-back dimension -- there are variations between current manufacturers, and between current production and older models.
What we do know however, is that almost without exception everyone who has adopted 0-MF has been delighted with the results, running a variety of different wheels.
Older wheels tend to be set to 29.0mm back-to-back, with thicker flanges (1.0mm max). Current "industry standard" wheels are usually set to 29.2mm back-to-back with thinner flanges (0.8mm max). In all cases the BEF dimension must not exceed 30.0mm.