In a similar situation, I added a third controller to go with the added panel. I have three controllers for three arrays on the roof all controllers in parallel to the battery bank, all set to the same voltage so they add their amps. Works great.
I got it that way from taking the solar sets from my previous RVs and using them with this RV so it seems like a hodge-podge, but it actually works as well as doing it all in one from scratch.
Generally, if there isn't enough sun for a bunch of solar to get it done, then adding more wattage won't help much. No sun is no sun. As in if there is no wind, hoisting more sail won't help.
It could make a difference in some scenario with lots of "dependings"