funny enough to the "put em all in middle", no matter how many times I tried, I noticed the best solution for me was 3 in middle two on the bottom.
Run it few times like this and noticed that the Teleport nodes combined with the RNG allow for better spread of the girls this way, thus covering more ground (is it not infuriating when RNG sends 4 of 5 girls in the same bloody direction ?) and having better chances to complete the mission.

Also what was necessary was to use my secondary parties (in tha Unit menu you have buttons 1-9 which allow you to make different sets of your parties). I had to use much weaker girls to make sure to maximeze the number of "runs" the girls can do before one of them hits home and recalls of the rest to her. Allowing 2-3 parties get wiped on the boss while the others managed to get on the right routes while running allowed me to clear this map very fast once I figured out the trick.
It was similar to the previous event map, where you had to tone down the strength of your army to avoid beating the final boss to fast and finish the map before all goals could be achieved.