Refer to these articles when measuring the armscye( https://sewandso.wordpress.com/2014/10/29/definition-armscye/ ) and sleeve:
Compare the measurements of the armscye to the corresponding measurements of the sleeve curve.
The sleeve curve measurement should be at least one inch larger than the armscye measurement overall. Each half of the sleeve should be at least 1/2 inch larger than the corresponding part of the armscye.
Otherwise, the sleeve will not fit in this opening, nor will it fall correctly on the arm.