Cucumber mistery!

We planted our cucks in morrisons pots last week and put them on the floor of the greenhouse on gravel.The ones in the center of the greenhouse are romping away but the ones on the side are half the size!Same care and temp.The only thing i can think is the ones in the middle possibly get a tiny bit more sun in the morning!!Any ideas please.

Well i never  Thanks for that DD i never thought of that one.They are all moved to the center now until they need tying up!