When passenger and shoot, you have some OP advantage:
- your damage is the same at any distance, unlike if you shoot onfoot, where at medium and far distance you damage is reduced,
- your hitbox becomes extremly small, only your head is vanurable,
- you don't have any recoil, which makes it a lot easier to hit target,
- you move a lot faster (ok, this one is fair),
- you are invincible when you are aiming if you are on a bike, or if in a car, but aiming to opposite side from where you sit due to not having hitbox. This one especially powerfull when abuse innocent drivers aganst cops.
I suggest neutralize the first mentioned advantage by making passenger driveby damage proportional to distance, like when you are on foot. Suggested damage values are in the attached table.