Miraphone rotor casing info

[iiipopes]

OK, we all know the standard Miraphone 186 rotor bore is .772, and these rotors and casings have been made since the beginning of the factory.

My question is about the 282. It is listed as a step bore .772/.803. Is the 4th valve rotor on the 282 the same casing with just the rotor bored out larger and with larger tubing connected, or is it, and the rest of the 282 rotors for that matter, a completely different rotor and casing?

If it's the same casing, etc., I wonder why Miraphone has not considered using the larger rotor, or if they have considered it, why they do not use the larger rotor on their 4th valve. After having my 186 now for a time and learning its quirks, I, for one, could use a little less resistance at that point in the valve block.