I don't get the 1:1 thing. It doesn't really matter what the ratio is, so long as it is a ratio that is communicated clearly and is not alterable, yes?
Yes.
Most people use 1:1 ratio whe explaining sc just for the simplicity of it.
1:1 means you get the same amount of bitcoins out as you put in for the same amount of SC. It means the SC doesn't inflate in relation BTC.