What do you think about it being deeper so that when sitting its at head level.
Well you COULD do that of course, but then you'd better have a backhoe and a six wheeler to dig and haul the spoils with! It would have to be 6' from front to back, and at least 4' wide and 4 1/2' deep, and even with that you couldn't draw and shoot from the side, as 4' isn't big enough. In fact, if it were that deep, you'd also have to dig it deeper and put floor boards in it, because it will ALWAYS have water in it. I've dug, built, and hunted out of enough goose pits to know that. Keep a 5 lb empty coffee can in there to bail with also. A pit of that depth will also require that you build a plywood box, so that the sides don't cave in on you after that first good rain.
A pit of this size would require you do excavate 4 cubic yards of earth, which will translate into 6 cubic yards that you'd have to haul away due to the "fluff" factor of excavated dirt.
It would be as snug as a down comforter though, and your scent issues will be minimal.
If you still want to do it, let me know and I'll give you some construction tips for the box. Like I said, I've built a few goose pits over the years.