Actually, starting all top or bottom is not necessarily the best idea. In that map, starting points only matter to slightly control the lenght of the path the teams take. I your probles is that your helper is slighly too fast, then all top (all teams have the same path lenght) is not too good. And all bottom is even worse as the helper team is going to be one of the 3 squads to take a short route.

Try to assure your helper takes the long route by starting up or being the second or fourth team bottom. Meanwhile, try to make your other teams take shorter routes. For those teams that will always take the long route, you can try the middle one for a chance to shorten.

I would go with 3 out of 4 teams down (2 teams take short route, 1 takes long one), 1 out of 4 middle(ony way to get it to short route is getting lucky) and helper up (long route). Luck is still required due to that random arrow though. ._.