I'm sewing up a top for Faire from a Simplicity costume pattern. Yes, yes, I know, not particularly hstorically accurate, but it's fun, and the first real pattern I have done.
The sleeve caps are different shapes. Meaning, one side of the cap slopes more than the other, creating a distinct left and right sleeve.
Only problem, which is which? Does the side with more fabric go towards the front or the back?
Look for the little triangle thingys on the cap of the sleeve pattern. They will match similar little triangle thingys on the armcye of the garment pattern.
Okay, so more fabric to the back. I'll try to remember that for next time. :D
the other way to think about it is like this:
when you cross your arms, where would you need the extra fabric? if you have them in the wrong spots, the back shoulder area will be too tight and their will be too much fabric bunched up in the front part of the armpit.