If they are faster than Horse speed, it affects the whole team. So the answer is YES.

For the good result, you need 2 Fire users with Hot Fire and 1 Water user with Shrink. How bigger damage, how higher EXP. A water users with Shrink is a great help, because it can make your damage doubled.

Look:
4 Fire users with Hot Fire: 4x3 = 12x normal damage.
3 Fire users with Hot Fire and 1 Water user with Shrink: 3x3x2 = 18x normal damage.

That is why that the Shrink is a great help for your exp. But it is a bit unfair for wind and earth users. They also want to train in the Goddess Training. That is why we often used 2 Fire users with Hot fire and 1 Water user with Shrink in a team. That free slot is for Wind and Earth users.

2 Fire users with Hot Fire and 1 Water user with Shrink: 3x2x2 = 12x normal damage, same as 4 Fire users with Hot Fire.