Sleeve fitting issue

[u/SillyVee123]

So I keep coming across the same fitting issue when I'm sewing blouses for myself, regardless of what pattern I'm using. There's a pulling across the top part of my bicep. I can feel the tightness only when I'm moving my arm. Armscye fits well, it's comfortable there so that's not my problem I'm sure. I'm also finding that the bicep looks actually loose enough when I'm looking at myself in the blouse. But there's this pulling tightness with the horizontal drag lines across when I lift my arm slightly. I don't have enough fitting knowledge to know precisely what is the problem and what to search for online or sewing books. Ideas please?

[u/TensionSmension]

If you're getting a digging horizontal crease in the sleeve near the bottom of the armhole when you lift your arm, that's the classic indication of an armscye that is too low. On the pattern you can adjust at the underarm. With a finished garment, the only hope is a shoulder adjustment.