Pot sizing for S/H

[kavanaru]

I think I have read somewhere (not sure whether here, at Ray's or at another forum) that the right size of the pot is not as important when S/H than when using other media. Especially not in those cases using a size one or two number higher than what you would normally use with "standard" growing medium. I am now about to start changing some plants to S/H, and am trying to find again where I read it or whether I just imagine it: No success so far!

My issue is that I have two pots not yet assigned to any plant (6'' and 8.5'') and a Brassia which is currently growing in a 5.5'' pot. The 6'' seems to be a bit too tight (5 new PB are starting to grow) and the 8.5'' too big (this pot is hughe: 8.5''X8''). Any suggestions? Am I right assuming that overpotting would not matter too much (appart from wasting too much water )