You should scale by laggedmovementvalue as well. When in slowmotion styles in bhop, you go up just as fast as you would in normal.
e.g. ScaleVector(vecAbsDir, GetEntPropFloat(other, Prop_Data, "m_flLaggedMovementValue"));
EDIT: If anyone else wants to fix this change line 130 to:
PHP Code:
newVelocity[2] = newVelocity[2] + (vecAbsDir[2] * GetTickInterval() * GetEntPropFloat(other, Prop_Data, "m_flLaggedMovementValue"));
Scaling entire velocity by the laggedmovementvalue makes horizontal boosters go slower than normal, they seem to work fine without any edits (maybe because it's applied to BaseVel?) so should only be applied to vertical velocity.