Havent received my first order of antenna, than I ordered a new one (same). Received it 2 days ago, sadly no improvements over stock one, actually its even worse signal (I have done measurement with wirelesmon). Looks like indeed aluminium back case is affecting signal.
una solución seria hacer un micro agujero en la tapa de aluminio y pegar una cinta plana metálica adhesiva a la tapa poniendo un aislante que actuaria de antena y no molestaría, encontrándose en el exterior
A solution would be to make a micro hole in the aluminum cover and to glue a flat metallic tape adhesive to the cover putting an insulator that would act of antenna and would not disturb, being in the outside