Query Regarding The Seat Availability in Between Stations

So i was booking a train from Point A to Point B , Point B is the terminating station here. A total of 31 seats are present when the booking window opens. But when the same train when returning from the Point B which is now the starting point will have 43 seats present during booking window opens.

Not only that, there is increase in other tiers as well, 176 instead of 120 in three tier .

I wanted to know what is the difference in allocation when its the same train and the booking is between the same two stations A and B