Yeah thats why i said irrelevant of the kit, a good point to start is a finger or two. If your kit is too low then compromise from that. But theres no way I think even a stock 34 will have a fist in between the tyre and the guard, four fingers at max.
Just as a point of reference, my 32 has the stock kit and front lip, and with 18" rims, there is room for just over a finger at the rears. And at the lowest point, the cat, it is almost exactly a 100mm off the ground with only the driver inside. I know this has almost no relevance to your car as I understand aftermarket kits can be very chunky, but I thought id just put it out