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.
Could you please explain to me why a fixed/time invariant 1:n ratio should inflate the native sidechain coin(1)? (serious question)
(1) I'm taking into consideration only sidechain where there's no other way to "introduce" sc coins rather than 2wp or atomic swaps (aka no coin rewards for new mined block only txs fee)