If you have a glass tube laser, you should just use the analog output of a controller for the power curve.
Even if you had software or a controller that supported PPI (that’s fast switching of the laser on and off while cutting aka Pulses Per Inch), that is a hard On/Off 5v signaling to the PSU.
This frequency setting you are referring to is something different and is designed not for glass tubes. It is for RF excited lasers (RF lasers). You should have it set to 20kHz and leave it. Otherwise, all you’re going to accomplish is disruption to the laser PSUs designed ability to effectively convert that PWM signal into an analog 0-5v signal.
If you’re seeing a difference from playing with that number on a glass tube, it is because your laser PSU is failing to accurately convert the non ideal or expected input.
Ruida controllers, for example, have and suggest the use of the analog output for this reason.