i've got a valentini and a clown together in a 20 g. w/ 40-50 lbs of LR
and they get along just fine. the valentini has never nipped at him or gone after him, even when the little clown rips food right out of his mouth.
i have snails and hermits in there and he's left them alone. when i first put him in my tank he immediately, like within 10 seconds, went for a snail and i thought, oh no, they're all going to die, but all he did was nudge it and he's never touched one since. i feed my tank every 2-3 days and the valentini still leaves everything alone.