[Kevan]

A motor pod sits on top of the chassis so you can't 'lower it' unless you remove material from the pod or chassis.

By backing the screws off you're allowing the body and chassis to move without affecting the pod and rear tyres, in effect the chassis drops slightly as the screws are backed off.  This will also lower the bodyshell so watch the tyre clearance in the wheel arches.

These are dead simple cars, don't overthink something that's blindingly obvious.