I agree in general with the "knuckles height". This has always been considered the best overall height for an anvil. It allows you to hit something about as hard as you can and still not be out of position.
If you are doing knife work and are forging from barstock or something similar, this is what I would use.
If you are doing something that is light or does not require a lot of full power forging strokes, you can put the face of the anvil a little higher. This will allow you to tap without having to bend quite as much. I do this for anvils that I use when I travel and do demo work. I only do light stuff and after 12 hours of work, it helps not to have to bend quite so much. A change as small as 1 to 1 1/2 inches makes a big difference. It goes without saying that if you end up trying to do something that requires regular forging, your wrist will not be in the optimum position.
I am not sure what size anvil you are anchoring but if you build the stand to the knuckles height, you can always slide a piece of 1/2 or 3/4 inch plywood under the base and see how you like the elevated platform. Assuming that you anvil is not a 15 pounder, you can just make two pieces of wood that fit inside the feet on the front (the side toward you) and back. If you fit these carefully, they will hold an anvil in place against any forward/backward or side to side motion. If you are bending heavy stuff in the hardy or pritchel hole, they don't hold that too well. The nice thing about these quarter moon shaped pieces is that they are easy and can be attached with a couple of screws to the base. If you want to try something a little higher, just take out the screws, insert the new base piece and screw them back down, simple. The anvil that I finish knives on is 1 inch higher than knuckle height. I don't do any heavy stuff on this and it is long and flat (homebuilt). I like it even though it is pretty non traditional.
Good Luck,
don't be afraid to experiment but remember that a formula that has worked for a long time has earned its place.
Jack