Long explanation of kick physics, courtesy of WCCC:

When the player uses the action button on the ball (frobs it),
it starts parsing how it was frobbed- which is to say, it checks
for duck level. If ducking it does high kick; if not ducking it
does standard kick. What determines a good kick is what lead us
to determine what the math and default values should be for ball
properties. It takes the player's rotation (not view rotation,
so this is to say mostly left to right or "yaw") and produces
the left/right value as a pointer, by converting the rotation
value to a vector value, or a 3d coordinate. From there, this
vector is purely forward relative to player facing, so our next
phase of applying math is to add the up/down factor of the kick.
So assuming the player's facing is no more than 1.0 in value for
either X or Y axis, we add 1.0 X FrobZMult as standard kick
height, and 2.0 X FrobZMult for high kick, which in turn
determines the ratio of forward-to-upwards direction and then
that ratio of up/vs forward and in turn what direction it faces
is multiplied by KickPower to determine the distance of the kick
with the relative angle of direction.

TL;DR How do I tweak it?:

-Ball will go higher relative to force applied with less gravity property.
-Ball will go farther AND higher with more kickpower.
-Balls achieves more height vs forward ratio from more FrobZMult.
-BumpMult is really just a multiplier for distance when ran into.