Thanks all for your help! I'm sure we will find a solution together!

I did some measurements and the situation is as below :



The bottom of the pocket is flat and the angles are not perpendicular to the bottom.

From my NON-experience, i may still see 2 options, please correct me if im wrong

Option 1 : I sand the neck pocket to make it all perpendicular to the bottom ?
Option 2 : I sand the heel of the neck to make

What do you all think ? is there any other option ?

Thanks