I read both sleep studies, and you clearly did not achieve acceptable results with CPAP. Using bilevel, you showed nearly no events with setting at 14/9.0, 15/10, 16/10 and 17/11. At 18/12 you had one obstructive events, and again at 19/13 there were no events, but sleep efficiency at the higher pressures is poor. Subjectively, your best results were at 15/10 with very good sleep efficiency no apena or hypopnea and very good SpO2 results.
Let's translate that a bit more. You are currently running your machine in Vauto mode at PS 1.6 in a range from 12 to 20 cm. None of the pressures currently being provided by your Aircurve 10 VAuto were tried at titration, but they most closely approximate the unsatisfactory CPAP results. At those pressures in CPAP titration (between 12 and 14 cm), you had AHI between 7.7 and 24 events per hour with mixed central, obstructive and hypopnea events. After 14 cm pressure, the sleep test moved to bilevel.
With bilevel at pressures less than 13/8, you had large numbers of events, and the titration demonstrated a "bright-line" minimum requirement for EPAP pressure of 9.0 cm to avoid obstructive events. Your current settings are above that minimum EPAP pressure, so your obstructive events are fairly well controlled; however, you are seeing centrals and hypopnea, which were eliminated by using pressure support in the 5 to 6 cm range, while you are using only 1.6. Although your current settings are not even close to your titrated pressure, you are doing surprisingly well, however, I recommend we get back to pressures and pressure support indicated by your sleep study.
I think you need to take a look at this bilevel titration and learn from it (see table at the top of Page 3). You need a minimum EPAP of 9.0 or 10.0 to resolve OA events. Your pressure support requirement to make other events go away and to make it easier to breath is 5.0 cm. Therefore in fixed bilevel mode (VPAP-S), you could set your machine to EPAP 9.0 and IPAP 14.0 and you should see good results. If you want to use VAuto mode, then your settings need to be EPAPmin 9.0, PS 5.0 and IPAPmax 17.0.
All of the setting options I have posted above, should result in better and more comfortable results that have been demonstrated effective by your sleep test. I encourage you not to over-think this. There is absolutely no need to guess or experiment with your pressures, these should work. I disagree with some of the advise you have received so far. There is absolutely no indication of a pulmonary issue or even central apenea in your case. Your reaction to pressure support, which in your case appears to reduce CA events, is not one we see very often, but based on your titration tests, you do better with PS at 5 than with PS less than 4. I want you to feel comfortable, and assured you can achieve good treatment at levels your sleep study demonstrated for you. Please give serious consideration to trying these settings and letting us help you to fine tune from there. We should not however attempt to use pressures your studies demonstrated are a problem.