[CPAP] Still tired after 4 months of CPAP

[Old Steve]

The only way to find out is to try it.  The problem with APAP is that it actually raises your pressure after you have had an apnea, not before.   Then it usually raises your pressure higher than you really need, then starts to drop, gets low and you have another apnea and it starts all over again.  The idea with CPAP is to not have as many OA's to begin with and help eliminate as many arousals as possible   If I remember correctly when I had my sleep apnea test back in 2000 the sleep doctor set my CPAP machine at 10cm.  That was back in the old days before CPAP's had APAP or EPR just a constant pressure.   Today I still run around 10cm in CPAP mode with an EPR of 3, so my exhale pressure is at 7cm.  I have run as low as 8cm pressure with out much difference in AHI.  Unlike you, I am used to higher pressure and if I run at 8cm or less I do not feel like I am getting enough air.    I sleep on my side and my AHI averages 0.50 or less.  If I start sleeping on my back in the middle of the night my AHI is a different story.   If your doctor set you at 8cm and assuming that he figured correctly it should work okay in CPAP mode too. Anyway, if you do not like it in CPAP you can always switch it back. 
The trick with sleep apnea is trying to find a setting that actually makes you feel better.   

[Phaleronic]

I'm with Steve on this, CPAP ended up being great for me as well, I have it at 15.5cm with c-flex on 3 and I'm under 1 ahi and sleep very well when compared to APAP mode.