Set in sleeve with no bell curve

Hi, I am knitting a child’s sweater. My finishing directions are: Sew shoulder and Sleeve seams. Set in sleeves,sewing top 1/2 in of sleeve along bound-off edge of armhole.
Here is a diagram


There are 5 BO stitches at bottom of armhole.
I’ve set in sleeves with a bell curve top and side seams open, not sure how to do this and the 1/2in instructions. So it’s just a circle to a circle. Do I still do mattress stitch seaming on right side?
Thanks in advance.

Yes, you’re seaming a circle to a circle. You can use mattress stitch from the right side if you like.

I don’t understand lining up the top of the sleeve with the bound-off edge of the armhole. Usually you would line up the armhole bind off with the sleeve seam. That way the sleeve seam is to the inside of the arm.
I would line up the middle of the sleeve bound off edge to the shoulder seam and line up the sleeve seam with the bound off edge of the armhole. Clip or pin in place and then pin the areas between these two in place to make sure it all fits easily.

What is the name of your pattern?

Cable-Dip Cardigan
Thank you for your response.

Intricate and beautiful cardigan!