They all seem to like different parts, and it can change with age.
Try putting smaller amounts in, so if he wants more he'll have to eat the stalks as well.
I've gotten to know mine chins and some chins get small amounts of hay while others get enough for 3
I wouldn't worry too much, I have one old gal who never ate much hay her whole life. She's going on 14 now, and has never chewed much at all.
Now if one of my normal chewers stopped chewing I would worry.