Tube is not square to the gantry or chassis. Best way to level the tube with the stock mounts?

So here’s the brunt of my situation. I leveled the machine and checked that the gantry is also level. It’s not perfect, but it’s pretty accurate. That said, I. Started checking my mirror alignment again because last night’s project was an utter failure. The issue I’m having is that on mirror 2, the dot is higher near the front of the machine (closest to user) vs the back (closest to tube). I can get the vertical alignment pretty solid so the test fires don’t move to the left or right when comparing. So my conclusion is that the beam is angled upward as it travels from near the tube to near the user. I raised mirror one with washers with the idea that I would angle it sharper downward to balance things out. But raising the mirror’s height had no affect on the upward traveling beam. The only conclusion I have at this time is that the tube is not level. I placed a level on the tube and determined it is not level. Core question is, am I better off raising a mount with shims or washers to raise one end of the tube to make it level or add something between the rubber and mount under the tube to raise one end of the tube? I’d imagine the tube can get pretty warm during use, so I want to make sure whatever is currently used to protect the tube from the mount is the only thing touching the tube if I were to raise one end by adding material inside the mount under the tube. Are ther materials I should avoid or are there specific ones to use for this purpose? I’m not sure what the best move is to avoid breaking the tube as well as not melting or damaging anything else in the mounting area. Suggestions?

Yes, It’s very likely that the tube is not in plane with the gantry. I’ve had that issue as well. It would be nice if the k40 came with adjustable tube mounts. You can either shim up the mirrors as you have done or try shimming the tube. The tube shouldn’t be getting any hotter than 25C or you have some other issue. So any rubbery material should work for shimming the tube.