[Scythe Kaze Master 5.25]A fan increases, the other one decreases

[SPN]

Hi!
I've just bought a Scythe Kaze Master 5.25" black fan controller and connected the 2 Corsair H80's fans (120mm, one per channel), which have a max power consumption of 4,2W (0.35A*12V). Anyway, when I set fan speed to max level, I find both the fans reach max 2130-2160rpm instead of 2500-2600rpm, and only if I decrease the speed (or just turn off) of one of them, the other one reaches 2400-2460rpm. I connected a third fan to another channel, but it only reaches 1050-1080 rpm max, instead of 1600rpm, but turning this off, it does not influence the other two fans. I measured the voltage to the power cable and I found exactly 12V, so this is not the cause. I'd ask you if this situation of "increase-dicrease" is normal, or not. And, in this case, what I could do. Thanks in advance for your support!

[SPN]

Anyone? I need to know what I should do (i.e. if this is normal or not). Thank you