It's much simpler than that.
Scottish football teams fall into just 5 categories:
1. There's the super-rich teams (Rangers and Celtic) who will always play in the SPL.
2. There's the big teams (eg Hearts, Hibs, Dundee Utd., Aberdeen, generally from cities of 100,000+ population) who will normally play in the SPL, however, the occasional crisis may see them relegated to Division 1.
3 And the quite big teams - that's us folks, along with the likes of Falkirk, Dunfermline, St. Johnstone, generally from towns/catchment areas of 50,000 - 100,000, which will frequently flit from SPL to Division 1 and back - the SPL/Div.1 bias being generally dependant on the size of the town/catchment area.
4. The medium teams - pop./catchment area 20,000 - 50,000 - division 1 or 2 (see above)
5. The wee teams - Division 2 and 3 with maybe the very occasional foray into division 1.
Sorry folks, but that's the rules - don't wish to appear negative or anything, but no amount of singing or shouting is going to change that! :)