i just gave another try the acrylic lens and now i clearly remember why i didn't like it,it still has a faint reflection box near the dot,i'll upload the photo tomorrow because i need to sleep for now.
Yes, the housings for the acrylic lenses is very short. I use fingernail polished applied to the focus ring and turn the lens until it just catches. Then I turn it upside down to allow it to dry. This gives me enough length to have "infinity focus" before the focus rings grounds out on the module. You will see more splash with these lenses, but I can see no rectangular artifact with them. And at distance, the splash doesn't matter any longer.