I've heard a lot of these rules of thumb for getting push to connect fittings to hold reliably. We've worked at trying to cut tubing square, pushing the tube all the way into fittings, and throwing out any batch of tube we thought was failing repeatedly. There's probably more we can do for quality assurance, but at some point I have to step back and think "there has to be a better way".
If barbed fittings reduce the id to much, another option is compression fittings with support inserts.
https://www.mcmaster.com/#compressio...ubing/=151zg0i These should be more fault tolerant than p-t-c fittings, and more easily removed than barbed fittings. But it would strip be a pain to work with two wrenches in the confines of a robot chassis.