Hello, T N C. Why do you want to prune it? It seems to be doing fine. I do not see a problem in the picture but distances are not obvious sometimes in 2-dimensions.

There is typically no need to prune a hydrangea and new stems are weaker at trying to hold blooms upright.

When pruned, some established paniculatas -for example- come back fast and furious. Which variety is this one?

I don't know what it is, I am just wanting to maybe scale it back slightly. So then I wouldn't hard prune, but just take it back some possibly? I like the height.

The only thing I noticed was that it seemed wider than taller

IME, pruning Hydrangea panicula really doesn't create a shorter plant; they regrow quite vigorously, even if pruned to just a couple of feet. You could try removing a few of the sideways stems back to the branch they come off of to shape and make them narrower, but I don't know how long this will last.

At the conclusion of winter, try reducing the radius by 50%, cutting out small or flimsy branches. I personally like the current size shown, so you'll probably want to keep it cut back in such fashion at least every other year so it doesn't get too big for you.