Sounds like your pressure settings are not set for best results, How long have you been using this machine and how were the pressure settings derived? A titration study by a sleep doctor? IF that is the case, the study needs to be redone but the results need to be discussed with the doctor who made the prescription.
I don't want to criticise the work of a fellow sleep tech without all of the data to hand, so please take the following with a large pinch of salt. Having saifd that, your results say that you are getting a butt-load of central (AKA clear airway) apnoeas. These are corrected by the difference between your pressures (and the timing settings but I don't know what they are), which indicates your machine breathing in and out to fill in the gaps where your muscles aren't breathing. In you case however, the difference between your pressures is just 4 cmH2O which is very low. It just may have been effective in your sleep study, but it would be extremely unusual if this were the case. Setting a BiPAP properly is quite complicated and very few people, even amongst sleep techs, know how to do it. I don't know how the system works where you are, but it may be worth you asking some questions to see how much your sleep doc and the staff at your sleep lab really know about using BiPAP. If you are not satisfied that they are experienced and competent you may need to go somewhere else.
When I was prescribed a Bipap vs another type machine, I asked why. I didn't hear any of the issues you bring up but was told that since I required the highest pressure (25), it made exhaling easier with a lower (21) exhale pressure. Guess I was getting smoke blown up my nose?
I am guessing that you have BiPAP for 2 reasons, Wiredgeorge. 1) If you need a pressure above 20 then you need a BiPAP because CPAPs only go up to 20. On a side note, a BiPAP can be set to work like a CPAP, so if we need CPAP of 20 - 25 we use a BiPAP set as a CPAP. 2) Comfort. It is usually assumed that a little variation in pressure makes for better comfort. In my experience this is not the case for the majority, but it can help in some cases. It works just like EPR really. It is worth noting that at settings of 25/21 you are getting the equivalent of a CPAP of 21, not 25.
As I mentioned above, few people fully appreciate the intricacies of BiPAP. That goes for doctors as well as technicians, so it's possible the people that set you up didn't know that much about it. I am privileged to work somewhere that has given me the chance to do hundreds of BiPAP studies, and develop some very specialised skills and knowledge.