I have a friend, 6'5 300~lbs. We had a rain and it softened the trails a bit. It was great riding conditions for me. He was complaining about his front tire sinking into the dirt, making the ride no fun. He said it primarily happens in the corners.
Is this a common problem with bigger boys? He is a new rider and riding a HT. My only thoughts are that maybe his front shock needs some adjustment or he could be keeping too much wait forward.