Controversial topic ... yes. If your LO sleeps better that way, they may have a reflux-like problem.
My SIL has a REALLY spitty baby (probably has a form of reflux but never been diagnosed) who has never slept on her back. SIL found that the baby wouldn't sleep on her back as an infant, so put her down on her front. Baby sleeps great.
You need to do what works in your house. If your LO sleeps better on their stomach, then go with it. They are getting sleep, and in good chunks. If you feel you need piece of mind, I agree with the previous poster that an apnea monitor would be a good idea.
I don't think you are doing anything that is out of line with your LO's biorhythm.