The room over the porch has the following problems:
Parts of the floor are soft--there even seems to be a hole under the carpet. Probably needs some of the subfloor replaced.
The front half of the room slopes downward, because it's over the porch and the joists run on a slope there.
Off the top of my head, with no experience and no real study of the problem, I decided that SLC is the wrong way to fix this. Instead I'm thinking I'll take the subfloor up; sister new joists to the level AND sloped joists, long enough to cross the room and tall enough to account for the slope; and then lay subfloor on top of that.
The end result should be level floor joists spanning the whole room sistered to both the existing level joists and the existing sloped joists. I can throw insulation into that above the porch. On top of that I can lay new subfloor and hardwood finish.
If you can't explain why, then you don't know what you're talking about. I'll keep asking until I find someone who does.