Horribly delayed and painful realization, but I bet the reason Dirk crawls onto a bed and assumes a submissive position the very moment he hears Priest’s voice is that he was punished in Blackwing if he was not on his bed when people entered his room to perform experiments on him.
This might also explain why he likes sleeping on the floor, because the floor is not the place where people drag him away into horribly painful experiences.
The floor is safer than a bed will ever be.
This is why Dirk’s response to being hunted by the Rowdy 3 was to dive for Todd’s bed.
Blackwing left him with precious few ways to fight back but, at least until the conditioning kicked in properly, hiding under his cold metal bed was something he could do. It was a sign that he wasn’t completely broken. It never worked (he always knew that would never work) but he persisted until Mr Priest established some ground rules (namely, that whatever the scientists did to him would never be as bad as what Mr Priest would do).
It’s yet another coping mechanism that he can suppress for years but can never really forget.