Radar Detector Performance Adjustments

[Mr Q]

I recently bought a Cobra ESD-7400 and it barely picked up any X band signals (had to be in front of an electronic door opener to detect a signal) and no X,K,Ka signals even when passing by a dozen or more police vehicles at speed traps. I got a refund and then bought a Cobra XRS-9370 and it did pick up X and K signals from a fairly reasonable distance but not as well as an older Uniden RD-55 detector that recieved X, K and Ka signals.
So my question is, do brand name detectors have any adjustments that can increase the dector's signal sensitivity from model to model? As I do not have any schematics of any of the detectors I have owned in the past, I was wondering if any of you have seen this activity within any certain brand detector. My gut feeling is that such practices are used and wanted your opinions on the matter.
My present detector (Cobra XRS-9370) has 4 trim pots and I was wondering what the purpose of each was (VR 101-104).
Any help will be greatly appreciated.