OK since I couldn’t find a copy of the pattern to look at on the net. I would like to know a little more info. Is it a seamed sleeve or sleeve worked in the round ? is the shoulder end shaped ? straight ? or raglan ?
I will try to explain some fitting techniques as I was taught.
If the sleeve is seamed this should in most cases match up to the side seam of the garment or if it is not seamed the center side as found by folding the garment flat an marking where it folds in half at underarm.
If it is a sleeve worked in the round from the cuff up with no other shaping ( straight set in ) you need to either go by the knit in design or find a way to determine top and bottom, front and back.
I like to pin mark ( Safety pins work best for knits ) the top center, bottom center and front and back center of each top sleeve edge.
Match up the top and bottom of the sleeve and arm opening, now here is where most problems occur … the sleeve edge and the arm opening may not match up exactly ( one or the other may be bigger ) you will need to ease the difference in fabric so that one edge may be a little tighter the other a little looser. This differential may come in to play either front and back or only on one side. Make sure you are truly matching top to bottom, if anything ease more to back than front as this will allow greater freedom in bringing your arm together in the front.your sleeve top edge is slightly larger than your armhole edge, this gives a nicer appearance and more arm freedom in my opinion.
I hope some of this is helpfull. I personally hate finishing touches of any kind and avoid them as long as possible. Right now I am dawdling along on finishing a jacket for myself that has a lot of loose threads that need to be worked in