Setting the queue length on HP p410(i) controllers

The guys responsible for the DB performance tuning asked me to change the queue depth on the two HP p410(i) controllers of my DL380 G6 server. They want me to switch it from automatic to 64. Unfortunately, I can't find a way to do it.

I've tried to bring up the array config CLI and type:

controller slot=2 modify queuedepth=64

and I got back:

Error: This operation is not supported with the current configuration. Use the
   "show" command on devices to show additional details about the
   configuration.

(Same thing with the slot 0 which is the embedded controller)

Any idea ?

OS is Windows 2008 R2 (x64), the ACU CLI version is 8.50-60