My understanding is that the OP wants the bubbles when they intersect to instead merge into a single, spherical larger bubble, and not intersecting bubbles. Perhaps he simply worded it poorly.
My suggestion is that making it work like that would be stupid and it'd be better to have the GUI change bubble size at the cost of oxygen and power usage.
Perhaps "stupid" isn't the choice word to use, but I understand that his suggestion doesn't seem to you like the best way to accomplish the end result.
I think that cranking up the oxygen usage to make the bubble bigger makes sense...to an extent.
I think there should be a limit for two reasons:
1) The machine itself is a specific size and so are the oxygen pipes that supply it and therefore they should only be able to handle a maximum amount of oxygen.
2) In order to expand your project (which is why you need the oxygen in the first place) it should cost you resources, i.e. machines. I think it becomes too easy and inexpensive if all you have to do is turn up the volume of oxygen. Like most things in Minecraft, there should be an initial cost for your return (smelting requires fuel, mining wears out tools, etc.).
Those are just my opinions of course though. On the other hand, I also see a potential issue with having multiple distributors simply merging into one giant bubble. What is the bubble centered around? Would it center around one machine or would it be the average center point between all the machines within range? I could see it being the average center, but that could also be an issue if you need to place a distributor somewhere to make it center the bubble where you want but what if that place doesn't work (i.e. floating in the middle of space, there is a structure or other object in the way)? Just things to consider.