Hi !
I’m a bit rusty at the moment so I’m sorry if I’m not that helpful.
Have you tried making a cylinder in a 3d software and UV unwrapped it? You could use those UVs to make a texture to mask the top face off of you cylinder, or just add two different materials for the mesh, one for the bottom (however you want the bottom face to appear) and top faces and one for the rest of the model. Make the first material just a simple red color and whatever opacity you want on that and the second material just like you have on your original material. This way you won’t get the unwanted effect on your top face. I hope this was helpful!