Do all ALT (Smurf) accounts get the MMR of G1-P4?

I have 1 alt and I noticed yesterday that I had been getting placed in games (Norms) with a much higher MMR than my main account which is fine because it is good practice to play against ppl almost 2 tiers higher than me.

I am wondering if this is the way it always is? Or is it just any new accounts in general? How does that work?

Thanks