Where a seam falls for a two piece sleeve

[theresa in tucson]

I have a question for the experts.  On a two piece sleeve where should the front seam on underarm be?  I'm working with a McCall's Palmer and Pletsch pattern and on my first muslin the underarm seam lined up with my forefinger when my arms are relaxed at my side.  I made another sleeve and added a fabric wedge to the top sleeve and subtracted from the under sleeve so the seam lines up with my thumb.  I have a high round back, sloping shoulders and a moderate forward shoulder so I always need to rotate a sleeve a bit to remove wrinkles.  None of my tailoring books say anything about this.

[posaune]

In a two piece sleeve you see only a seam when you look from behind  - the seam which runs over the elbow. It ends at the edge of the palm.  The frotn seam is hidden from the arm.  It begins 2-3 cm from the side seam notch and ends  inside the palm. 
lg
posaune

[theresa in tucson]

Thanks, Posaune.  That tells me I need to modify my sleeve since the front seam line on my muslin lines up with my thumb.

[Henry Hall]

Thanks, Posaune.  That tells me I need to modify my sleeve since the front seam line on my muslin lines up with my thumb.

It must be a half/half sleeve in the British style. The one where the top seam runs to the inside (most sleeves now) has a 'false forearm'; an addition to move that seam to the inside.