Creating a PBD waypoint with an altitude constraint won't help.
If it is too close, the A320 will not try to make that altitude, just the contraint will turn amber and the MCDU will display "Altitude error at WPT".
If it is too far, it will carry on until the waypoint before turning even if it is higher already way before.
You could find a distance at which you will just reach this altitude, but it's not practical to do so as this distance will vary depending on aircraft weight, wind and all.