DX3r framerate setting for use with Castel controllers?

I was under the impression that frame rate applies to the signal output from the receiver (to the servo/esc etc) as well. It is the 20ms bit of the pulse that is being changed when playing with the framerate.

It can be set to 16.5, 11 or 5.5ms on the DX3r... Methinks I may have to hook a receiver up to an oscilloscope at work to measure the pulse output signal...

Plus, if it was just the carrier form the tx to the rx only, then why would certain servos not work with the faster settings?

Cheers
Andy