I am not sure of your specific combination, or what Kodak recommends for developer volume. A quick look in their data sheet (link) shows that they recommend use of stock developer or 1+1. I see no recommendation for 1+3, so hard to say what the manufacturer recommends. It's probably safe to assume, though, that at 1+1 dilution, there is enough developer in the solution when you cover the reels, to fully develop the film.

But, whether you develop with stock developer or diluted to 1+3, you should have enough developer in the working solution to develop the negatives to the same contrast. It's just that 1+3 gives you longer developing times (and that will effectively develop the shadows more than the shorter time required for stock developer). It also gives higher sharpness due to less solvent action, and it's a more economical way of using the developer.

Other than that I have nothing to add due to my inexperience with D76 in particular.