It could be that he's not ready regardless of his size. It could also be like somebody said above they wont always lock on their first intro. Also you wont always catch it. For instance my 1400 gram male enchi will do the deed for 24 hours at a time, but my male yellow belly at 900 grams will go for about two hours, and never on the first date.
But this is my first year too so I'm learning as I go. I've got a male lesser, and a male pastel in the 500 to 650 range that only spoon with the girls. Haven't witnessed a hook-up yet. So I think as there are a lot of variables the best thing that I have to keep in mind is what somebody on here said in another thread " They've done it for 1000's of years in the wild without us. Give them time and THEY'LL figure it out." . So basically try not to complicate it. They'll figure it out.
Hope this helps
Dustin