thanks for the great answer
i would have to agree that, as they always spawn in the same spot, i think these particular spawners are seed dependant.
after making the world a few more times and paying closer attention i noticed that it's the same 4 that spawn every time. the 2 that are missing are always the same 2.
in the original spawn they were both second spawers of a double spawn so maybe that has something to do with it?
I have no idea the rate at which double spawners will spawn as opposed to just a single spawner and extra cobwebs where the second spawner should be.
as i said in a few of the threads i made, none of this is very critical to me, i just find it an interesting way to explore some of the mechanics of the game without getting too deep into the equations and higher math that goes over my head lol.