A lot of people have nasal flow problems on CPAP. They've generally had it before CPAP but find it a real problem when they go on it. Humidity and increased pressure can help, the latter only if it doesn't make leaks worse.
If the normal things that generally help don't work for you, you need to get an appointment with a specialist. You need to be proactive and pester (gently) your doctor asking for more help with your nose blockages. Beware of surgical solutions because they generally don't help (though there are exceptions) and they are painful and take a long time to heal.
I've had nights when I thought my nose was too blocked and found the extra pressure almost always makes it possible to breath through my nose. Not everyone is helped this way.
Once again though, I suggest you need to actively insist on getting some help with this from the medical profession. If necessary a specialist needs to be brought in.
You appear to have an APAP machine set at a single pressure. Setting it in auto mode may help it increase airflow when your nose gets more blocked. Maybe run in variable mode from 10 to 15 for a few nights and see if that helps.
The above is my opinion. It is just possible that I may, occasionally, be mistaken.
I am neither a Doctor, nor any other kind of medical professional.
Everything put together sooner or later falls apart.
Your brain is not the boss.
Our forefathers took drugs.
He's no fun he fell right over.
This time of year can be especially daunting to sufferers of nasal problems due to the increase of pollen, as well as increasing humidity after the drier winter weather. I do not recommend (self-induced) increasing your pressure in an effort to overcome sinus problems. That theory should be approached after consultation with medical professionals.The increase may multiply your sinus problems as well as interfere with the prescribed pressure for your apnea. I've found that a nasal rinse with a saline solution induced through either a squirt bottle or via netti pot helps considerably before going to bed. There are many products available to use for relief. Flonase is a good product, but if it doesn't work for you then maybe something else in the antihistamine family will work.
Yesterday is history; Tomorrow is a mystery; Today is a gift; Thats why its called "The Present".
Has your ENT had a good look in your nose? If you have blockages or large turbinates you may need that fixed by surgery before you can benefit fully from the cpap. My father in law had to have multiple procedures done before he started using the cpap for it to help him fully. He's the one who recommended the ENT/Sleep doctor I started seeing. He looks at the big picture and doesn't jump right to the cpap if there are physical obstructions.