Auto upgraded SL to 3E

Travelling Dewas to Ahmedabad - 20936

Why do we not get the same berth preference if our ticket gets auto upgraded. I had a SL in S5 but now I'm in M1 due to auto upgradation and got a SU.

I am not complaining (as I can say that I liked the M1 coach in here) but I do not know why I always get the seat near to door on either side of the coach. I'm tired of that. Is there any algorithm that allots the berth as per the number of passengers travelling. I'm single traveller.