Some machines have limited space for laser tube mounts. To put in a large diameter laser tube, it is ok to raise one mount higher so the laser beam can hit the first mirror. Just be careful about air bubble trapping in the water. It is not necessary for laser tube to be leveled to align laser beam. The first mirror can be adjusted to make the laser beam parallel to the machine gantry. Actually, some laser tube manufacturers recommended raising the laser output side higher to avoid trapping air bubble.
Some machines mount the laser tube on the side with rubber
pads. If you want to put in a large diameter laser tube, you may use thin rubber
pad on one of the mounts, so that the laser beam can hit the center of the
first mirror. If the first mirror mount can be moved paralleled to the gantry,
you may not need to adjust the tube mounts. The mirror mount can be placed close to the laser tube. However, if they are in contact, the mA will be low; laser tube cannot fire correctly.
If you do not have a 3d printer, you can still custom make an adjustable tube mount easily. For example, bending a piece of sheet metal into triangle, then put soft pad on it. The laser tube height can be adjusted by changing the distance between two triangles.
For a long laser tube, depending on its design, tube mounts placing at designed positions can minimize the laser tube bending. It is hard to see the small amount of bending by the laser tube’s weight, but it can affect the laser output power. For a laser tube shorter than 1850mm, it will not affect much if the tube mounts are a few inches off the designed positions.