symm optimizer across different rpm's

Just finally getting around to setting up optimizer on our dmx4-24 with code 5722. This is different from prior symms in that it has both 10k rpm drives and  15k rpm drives. I don't want to swap between the 2 speeds. I know I can create lists to segragate those disks in the optimzer but I found this to be a pain. I've not seen it documented but it appears the optimizer won't actually suggest a swap across differing rpms - I say that because in attempt to create the lists I get errors if I accidently put a 10k drive in the 15k list (and visa versa). Am I right about that?