I told my GP exactly what to put on the prescription. It included type of machine (APAP) and the settings.
If you have a good enough relationship with your GP then do the same. I'd convinced mine that I knew more about CPAP and it's treatment than he did and he agreed with me.
The change of machine revolutionised my treatment.
Go for it. GPs are good guys but they don't know everything.
I agree with the others.
If you can run SleepyHead and have a data capable APAP then
there is no rocket science to setting your machine to the proper pressure range.
The folks here can help you with this as well.
"With ordinary talent and extraordinary perseverance, all things are attainable." - Thomas Foxwell Buxton