Gladiators beast being attacked while being facedown

Well, I had a duel with someone who argued that gladiator beasts effects don't work when attacked face down... is that true? Like if a monster attacked my face down hoplomus.

sure they work...
the only condition they have is, that they must survive a battle (=going through damage calculation) they don't need to be face up at attack declaration.

Hmm, that sucks, I can't believe I got an ASS all because he didn't knew that.