Yet another jacket fitting thread...

[jruley]

Well, it sounds to me like you could let some out of the front shoulder and take some from the back shoulder.  But I'm just an untrained amateur.

[peterle]

You could probably do the iron work with just snipping the basting but I think it is not very handy. When doing ironwork with double layered fabric don't forget to flip the material and repeat the process to the underlayer.

Jruley is right:
Front balance: the vertical distance from the chest line to the neck point.
Back balance: the vertical distance from the back chest line to the back neck Point.
Nativ speakers please don't be shy and tell us wether there is a more common term in English?

To lengthen the front balance slash your paper pattern horizontally and insert a 1cm strip. Best level is at the most narrow spot, where the "stretching" has the least impact to the armhole curve.
Same for the back, but you have to take out 1cm in your case.
On your cut fabric pieces you just lay your paper pattern on the fabric and shift it 1cm up (at the front) and remark the gorge-neckhole-shoulder line.
Same for the back, but 1cm downwards.

The reason for the front/back distribution is to keep the given scye size and circumference. Just shortening the back balance for 2cm would also shorten it's size and circumference.

[Dunc]

OK, thanks Peter, I think that all makes sense. Much appreciated. Obviously ripping it down, making the adjustments, and basting it back up again is going to take me some time, but I'll update with how I get on.

Thanks again for your time and patience. 

[peterle]

Sorry, no shortcuts in tailoring.

When you do the ironwork first lay the same pattern pieces precisely onto each other and do it double layered. Thus you make sure both pieces get stretched for the same amount.