Monster spawn probability?

[Hero30]

Do different monsters have different chances of spawning? I know they won't appear until their initial spawn room but after that is there some sort of algorithm to when they reappear or is it all equal chance? Because I've gotten Specimen 6 chasing me FOUR CONSECUTIVE TIMES!!! Four times in a row from room 600-900, with no different monsters (I of course faced Specimen 10, 11, and 12 in their respective areas but no monsters spawned at random except for stupid freaking Specimen 6). It is get really annoying and ruining my enjoyment of the game as A. I'd like to have some variety while playing and listen to some other amazing chase themes and B. I hate Specimen 6. It's not scary or difficult, it's just tedious to deal with as you have to moonwalk through twenty maze like rooms listening to his very slow song. He effectively can't kill you after you figure out his gimmick unless you let him and running into him exclusively is really starting to make me dislike the game.
So do the monsters have different chances of spawning or do I just have really bad luck?

[Ninjaboy5056]

Sorry, pretty sure you just have really bad luck.
I was mostly stuck with the Puppet, the Ghost and the Goo Man.