Sam will do this to me and I don't judge it as dominance. I think you really need to judge the situation in its entirety and not a single action.
For example, I will often stand in front and just to the side of Sam's shoulder and drape both my arms up and over his neck, which naturally places his head to my left side and over my shoulder. As I stroke his neck, I can feel him relax until at some point, his head is over my shoulder, with weight on me.
If I shift my body enough, he raises his head. He is not trying to move me or push me further to the ground. He is just that comfortable.
Same with the leaning. If I lean into him and we are obviously not working, meaning, it's all about comfort and affection, he will lean / brace into me while he enjoys the attention. As soon as I shift, or if I give him a cue to move to the side he immediately responds.
Before judging him as dominant, I would repeat the situation. Then, cue him to move from your personal space. How quickly did he respond? (First, make sure he is awake.)
I cue Sam to move by mimicking my leg on his side by gently nudging him.
I would say, enjoy the idea that your horse is comfortable with you to relax to that state of trust. If at anytime you think he is being too comfortable, cue him to move.