Issues with devices

Here is an issue that I have and would like to know if others have had this and what to do. I have a HT2 plastic, an a small metal device that I purchased from DH Gate. While wearing the plastic device I have an issue peeing. It takes a wile to empty my bladder while wearing the device. While wearing the metal device I have no problem at all. The ring size for both are the same size, the small metal cage is shorter only 1.5 inches, the plastic is 2 inches and a bit wider. Of course I always sit to pee, Wife's orders. So don't know why this happens. Looking for answers, so any good answers would be greatly appreciated.