Do you know what film they use? Just wondering...
Film rolls are usually in 50%, 35%, 20%, 5%.
When you go into ceramic, they go 60%, 50%, 40%, 30%. I have 30% Madico Advance Ceramic on mine BTW.
Anyways, if you said 30%, you probably got 30% when everything is said and done. OEM windows contain minimal tint, so when you put any tint onto a window..it will always read lower than what is on there.
For example, on my past car (325xi) I had 35% put on and it metered in at 32%.
This car, I have 30% put on and I just metered it today when I was doing my clear-bra and it metered at 26%.
When I worked tinting windows...it was a big no-no to touch anything in the car. We usually told whoever that was bringing the car to take everything loose out with them. Usually makes life easy when you're crawling in the back for rear windows (or in your case trunk).