It really depends on what you are shooting for, Eric (no pun intended). A deeper level means removing more wood from the stock, which could weaken it a bit, but then again, you have a lot of play in the front trigger it looks like. Myself, I like very little play in the trigger, whether a simple trigger or set. It also looks like you aren't going to get that much leverage from the single trigger mode. I think I would want the trigger set moved back a little bit more, to give a greater mechanical advantage, but I like a light trigger pull. But when using a double set like this, it may not be important. You can always use the set trigger and adjust for your ounces of pull.
Going deeper would give less trigger play, but would not help with mechanical advantage. Moving the assembly back would require deeper inletting for less trigger play, but would give better mechanical advantage. It really depends on what you are trying to achieve.
Most guns I make have a simple trigger made for them, meaning that there is no set or anything. They require about 8 ozs. of pull, so they are light, but not too light, and at 32 F, They have almost no play. Nothing against the set triggers, but unless you are building for target work, they are really not required, unless you are trying to make an exact copy of a particular prototype. Lots of Tennessees had a simple trigger.
This also requires that you think about the architecture of the stock... Will moving it up or back change things to a point where it won't be right? I think it is a hard question, but one that is absolutely solvable. You could also add or subtract metal from the trigger mechanism itself, to achieve what you are shooting for.
Matt