Fully agree that the traditional length would be at the fell line, and for good reason, however,... if that length is too short for the pockets to look reasonable, relative to the hem in the front, I would vary it a bit. I really think that nothing looks worse, nor screams "Do it yourself jacket" more than pockets that appear to be 1-1/2 tall, and exaggerated angular sporran cutaways in the front.

As was mentioned, play with the variables a little bit, take photos, chalk it, pin it here and there, then go with the compromise that looks best to you. Don't be in a hurry to have a poor looking final product.

That will be two cents please.

Best of luck!