In my experience:
1 mile will work really well
2 miles will probably work OK if you have higher gain client antennas.
3-6 miles will not work very well at all with these low gain horns in my experience.
As well, you’ll want to check the antenna beamwidth… I think Cambium is doing a UBNT thing with the “60 degrees” on the horns… that’s -6 db loss at 30 degree off-center I think, which means you’re down to less 5ish dBi gain near the edges of these horns. To be fair, these Cambium DualHorns are really targeted at short range and high interference areas, and for that they work GREAT. But it’s not really designed as a solution for SM’s out past 2 miles.
So… I realize that wasn’t what your question was. Your question was about channel reuse, and I’m normally hesitant to confuse the question with un-asked for advice. BUT, in this case, your channel plan might be immaterial if the clients no longer have enough signal, and they only modulate at MCS3 or MCS4 after changing the sectors out.