Ah I see. As Yogi Berra might say "if you had mentioned that you wouldn't have to tell me that again".
Yes I also like a comfortably wide spacing of the hands when casting with two-hands overhead. If you benefit from a mnemonic device (which I do very much) put the hands at least as far apart as the length of your forearm plus one fist. In other words put the bottom hand just below your upper arm's elbow.
Take a second to try that. Put the bottom hand below the upper arm elbow. Do a roll cast, a backcast, a forward cast, etc. Now put the hands closer together. Now wider. See what I mean?
There is also fishing to consider, not just casting.
I like a long handle to place under my arm while strip retrieving the fly. A short handle means I am holding raw graphite under the arm, or that the reel is in an awkward spot.
Moreover a big fly and often sinking line requires a roll-up move to get the head out of the guides and the line positioned on the surface for an instant between casts. The advantage of obeying what I call "the elbow rule" is that the roll up is comfortable and leveraged. You do one with every cast so that can matter.
The elbow rule is important on the cast as well. The bottom hand must never rise higher than the upper arm elbow
. If it does the rod angle will go flat and the rod will lose it's load. This is what Simon Gawesworth calls a "trunk".
Not to sound repetitive, but there is no single right way (unless you are teaching a beginner with no previous experimentation of their own). You may discover a very effective means of overhead casting with two hands butted up against each other, who knows.
But in general the spacing I mentioned above and the casting/fishing considerations therein were gleaned from much time in practice on beaches like Nauset on Cape Cod and are thus offered in the hope that they provide some insight for your own journey into two-handed casting bliss!