When attacker replaces defender he will use the defenders position when he supposed to play as attacker.

Example

In any match, any minute, if we are behind by 2, replace the player on zone D, side C and mentality 1 by (player X) on zone A, side C and mentality -1

In your example player X will use the newly specified position once he enters the match, zone A side C and mentality -1. The previous player position on zone D, side C and mentality 1 will be empty. If there is no player on the specified position no substitution is going to happen.

“In your example player X will use the newly specified position once he enters the match, zone A side C and mentality -1.”

The attacker is playing mostly on D C -1 instead of the A C -1 position.
Had several occations where the attacker was last man on the D C -1 position..
I almost thought he would take over the keepers position :)

That’s weird. I have to admit that when I was last managing a team I didn’t watch the replays so I’m not sure that happened with my strategies. We’ll have to test it again and make sure the sub player is indeed taking the new position rather than sticking to the old one.