Personally I find no need to actually measure the distances since I'm going to play around with the file alignment until things sound right anyway. Gives you a starting point I guess, but that's easy enough to find quickly afterwards without a measurement.
These are really three entirely different things: A SBD patch, an AUD pair in the back of the room, and either an on-stage or stage-lip pair. On-stage/stage-lip+AUD isn't really a close analogy for stage-lip+SBD or for AUD+SBD.
Is the AUD pair in back analogous to the SBD feed? Not many around here would argue that it is, they are obviously very different. The AUD has all the room and audience in it and a far more distant perspective on the sound from the stage. Yet in the case of on-stage+AUD, the AUD is what is going to provide the elements which are heard from the PA that are not picked up on-stage. Vocals are the most obvious thing in that category, but also things like anything going direct to the board such as acoustic instruments, or other stuff only weakly amplified next to the musician, which relies heavily on the monitors and PA. Unless you are getting that stuff from an on-stage monitor, it's probably represented very weakly in your on-stage channels.
Is the on-stage/stage-lip analogous to the SBD feed? Not usually, for the same reasons just mentioned. And that's why on-stage/stage-lip + SBD is often a good way to go when you are restricted to 4 channels. The only part not mic'd in that case is the room and audience, and you may get enough of that in your on-stage/stage-lip pair anyway and not care for more of it.