I can offer an educated guess, but it's still just a guess; most from watching some old dedicated tests, like from Vedui, and following plenty of youtubers over the years.
I think screamers require a terrain block and an open sky above. So the if highest block of a coordinate is dirt/stone/asphalt/ore, a screamer can spawn on it. The reinforcements work pretty much the same.
There's also some distance limits, but you'll have to be really deep to avoid a spawn that way.
So, for most "shallow" mines, the screamer will spawn on the surface and all the adds as well.
The worst case scenario would be a long roofless drop from surface; the bottom of the drop might end up being the only spot where the screamer and the adds can spawn. So they will all spawn there. Of course that can be trivially turned into a best case as well ..
Plenty of caveats; just a couple
- I'm not sure of the sky requirement, but it would match all of the data I can remember seeing. Small exceptions may apply, like for plant growth, the sky requirement is an area, something like 7 blocks around; the same could apply for spawns, but I don't find that likely.
- Are some blocks considered "transparent" for the sky requirement; for plants some are. Hatches having been one, historically.
- Something like water; no real idea. A large body of water will prevent horde spawns entirely, and I do assume it prevents all other spawns as well.
- Things may well have changed, or get bugged, or the usual ..