My son is 21 months. He can sleep with and without blankets no problem. But when he has any blankets I usually allow multiple hospital like baby blankets. If he isn't snuggling to them then they are laid next to him. In exception of one. He has to have one blanket cover his head when he goes to sleep. He won't fight over me moving it but I'm concerned if I need to real worry or if it's just a "him" kinda thing.
I would not worry too much about it. My son did roughly the same but a little older, around 3 or 4, and with a full comforter. I'd go pull it down after he was asleep and his hair was all sweaty but otherwise he was fine. He still likes to have the blankets up to his neck even when they seem way too warm to me. His siblings mostly kick them all off. I had weirder sleeping habits when I was a kid myself. So I'd say it's just his thing.
If you haven't done that already, you could try leaving a night light. Perhaps he's scared and feels safer under the blankets.