So, here you are, the change you made in the back makes an improvement.
Don't get ahead of yourself by doing too many things at once.
Redraft the neck using an alternative formula. 1/6 chest is really more appropriate for jackets. So you could try 1/5 of you neck measurement instead.
Yes the across back calculation of 1/12 chest plus 1 1/2" controls the shoulder seam length.
But, The next thing to do is figure out how much width you should have in the back.
So do you have an across back measurement of your body? Compare that number to what the draft gives you using their formula. Generally you will want half your measured cross back plus some ease. Since this is a close fitting shirt block, then half cross back plus maybe one inch? No more.
If you redraw the back of the draft narrower and keep the total circumference at the chest you are shifting the distribution of fabric by shifting the armhole laterally, giving more fabric at the front of the body where you need it.
So to recap, redraft using a better neck calculation, and a narrower back.
The next stage as Posaune says is balance. The front needs some more length and a little more width at the waist because the front of your waist sits forward of your chest by a small amount.
So on paper, i would slash horizontally across the pattern at the chest line and open up a wedge say 5/8 " deep at the cf.
Using the CF line from the neck to chest, redraw your CF line straight, which will add width from the chest all the way to the hem. I think Posaune had a diagram earlier showing this. This is your new CF line, and set it on the straight grain.
Thats it for now...