The 6*2*2 could house a group of channa Pleuropthalma without any problems for quite some time.
The only time you'd see any fights would be, during summer, when the temps rise. A good way to keep the fights to a min, is to add a big boss man, a maruloides is a common peace keeper.
And the growth rate of pleuros is quite slow after they reach 11".
They will fight more often then just the summers , they constantly have small spats and typically no damage is done but as space gets tighter more of those spats will escalate into full out fights.
Mine have lots of space, plants , floating and sunken driftwood etc. and they still get scrappy every couple months. Typically it'll start with some flaring for a week or so leading up to a brawl , everyone gets a few torn fins , then they fall back in line like nothing happened for a few more months. The smallest one often gets a bit more beaten up & ends up hiding for a week to let his wounds heal before rejoining the group but he's a tough little guy so far he's still ended up back at the front of the pack once recovered lol.
I would strongly recommend against mixing channa species . That's a recipe for disaster . I doubt the "bigger police fish" of any kind is wise , my Pleuros are very bold they top/bully tankmates twice there size. Anything that ignores them typically gets left alone , anything that fights back or gets too active triggers all the Pleuros to target it.
I would put a pair of auranti in the six foot,the 4 foot i would stuck with some bleheri or assam!
Personally i would sell both tanks and get a 10 foot for a pair of micropeltes
It won't do any harm to give them extra space but my experience is that the subtropical species don't require or enjoy the extra space. I upgraded my breeding pair of Auranti from a 4' to a 6' and the only advantage was extra space for fry to grow out in before separating them. The rest of the time the tank looked empty , they built a cave in the fat corner that the male rarely left. The female spent her days in the floating cover above him . A year or so later I downsized them back to the 4' because they just weren't using the space And I have other species who were better suited use the 6' tank but they seem much more content now they are back in the 4' tank . The female cruises around again and male isn't constantly hidden in his.
I keep my bleheri in 3' tanks and it's more the enough room .
A 10' tank might work for a solo micro , but I bet a pair still too each other apart when they hit breeding age /size.
