Alright, I've looked into it.
The issue is that the combatant can't reach the target cell due to it's size, i.e. your changed maximum distance is the solution for this.
Generally, using a larger maximum distance with the Nearest target cell will move to the nearest possible cell to the target, so taking the largest size your combatants can have should do the trick, e.g. in this example, a grid size of 1 means it'll need a maximum size of 2 to take the extra cell around the combatant's actual cell into account.