Jerry,
I make all my dovetails .030" deep and per L C Rice on their 12L14 barrels he said .100" wall thickness between the bottom of the dovetail and the bore was plenty for the barrel tendons. Since the barrel tenon dovetails are closer to the combustion chamber than the front sight one I would think you could go less but I will leave that to others to confirm.
I use the little silver heart shaped sight for my fowler front sites and soft solder them directly to the barrel without a dovetail.
Dennis
