I would test speeds. And if at one speed, these artefacts are gone, I would use that speed for the outer wall. Stability comes over the inner walls, if there are enough. The melting temperature will probably also play a role.
I increased the belt tension on the CR-20. That did not bring any improvement there. Either there was no effect at all or a slight deterioration (dimensional accuracy or something else). That’s why I went back on the CR-20 with the belt tension and only tightened it so much that the belt was just tight. So I got the idea there to install tension springs to bring the belts to an equal tension where it works best. At that time I didn’t have an X1. When I got the X1, I saw that I was not alone with this idea. Increased belt tension increases the load on the motors and the pressure in the bearings, but it also stretches the belt. Therefore, the engine could run even more jerky and make the problem worse. And the dimensional accuracy of the pressure could be worse.
I would not handle oil. At high accelerations, I would be concerned that the belt might skip a tooth. But it could also promote an unclean pressure pattern if the timing belt suddenly becomes slippery. Oil always spreads, it never just stays where to apply it.