I saw a tutorial that noted the inaccuracy of wire lengths and sizing in Revit, and mentioned that there was an inherent flaw in the program. The suggested workaround was to DOUBLE the Max Voltage Drop values. The end result in the model should be lengths and sizes that more closely match what you would expect. However, calculating the true Voltage Drop would then have to be done manually.
Interestingly, I've yet to see anyone else identify the root of this problem, or offer a similar workaround. I can't help but wonder if Autodesk is going to get this fixed in an upcoming release. The info is not much good to you otherwise lol