The houserule work for agi 3 characters.... but has reduced effects for agi 4 (and agi 9, but nobody will get there 😅) characters(they dont get the benefit on full move, just on run/charge actions)
RAW: Agi 4 full move: 16 (4 squares)
Houserule: agi 4+1 full move: 20 (4 squares)
May i suggest to change it to "+1 movement distance square to full move,charge and run actions" that way the rule apply to every agi value in the same way