The easiest way I know to adjust the speed of the dust extractors with any sander is to run the sander with the dust extractor turned off but with everything hooked up. Noticed how the sander sounds and feels.
Then, turn on the dust extractor set on low speed. Turn it up until you hear the sander start to "load up" and feel different. At that point, you know you need to back off the speed of the dust extractor.
It's going to be different for each sander (mostly based on pad size), but as the grits get finer, it changes also.
In general with Festool sanders, you don't have to try to overpower the suction to get the best results.
To the contrary, most people who have poor results with any Festool sanders are either using a dust extractor that has no speed control, or they haven't adjusted the speed control, or they are holding the sander wrong (maybe even pressing on it).
I've found that until you get to pretty fine grits with a 150mm pad, you can run a CT 22 or CT 33 at full suction and it works fine. Smaller pads require less suction.
Tom is right on. The only item I would add to the list of reasons for poor sanding results is the skipping of too many grits.