I have been sewing for many years now! I used to get so frustrated trying to add set in sleeves until I came across this helpful tip; first stitch with regular stitch length from underarm area of sleeve to the notch.
This page contains the following solutions.
"Sleeve styles that are popular vary with fashion. Sleeves may be set-in, raglan, kimono, dolman, etc., etc. But whatever the style, there are some guidelines that will help you determine how the sleeve should look. The most popular style sleeve is the plain set-in sleeve.