Since I am the very meticulously responds to dust under the film and I would see this constantly in my white Xperia Z3C a candidate I deviated from the assembly instructions.
The guidance of atFoliX works very well but I just stuck the film underwater on the phone and afterwards with a squeegee (not using the enclosed map, which is on board and softens) all water and air residues eliminated. Keeps bombproof and I have no dust inclusions!
That's one of the advantages with a waterproof cell phone)
I have the atFoliX front and rear mounted and in addition the Case-Mate Barely There ultra thin protective case for Z3 Compact transparent in use and find it personally to protect the best combination to the unit.