The key point is that it is a worst case measurement so that entire BUMPER has to be compliant with the ROBOT sitting in the worst case orientation (which is an issue if you have an asymetric drop center drive or angled BUMPERS). The highest point has to be compliant, not the at rest orientation or the optimal orientation.
The other point to consider is that measurement techniques vary from year to year. Past year’s techniques or past event techniques in no way mean that the same technique will be used. For example FRAME PERIMETER may be assessed with a heavy duty tape measure, a fabric (read flexible) tape, or a piece of string. ROBOT size has been done with a go/no go rigid box, a tape outline or a tape measure and eyeball. Some inspections and inspectors allow for a bit of noodle compression to make it fit, some do not. Passing inspection at one event, does not mean you will pass at the next. If you are compliant worst case, to the most rigid interpretation of the rule, you are complaint. Anything less could result in unhappy time fixing your design at an event instead or being out in your practice matches.
For whatever reason, BUMPERS seem to be a source of ongoing trouble. I think I have seen at least one team rebuilding BUMPERS or BUMPER mounting systems at every event I have attended. Some of those have been due to woefully flimsy or poorly mounted BUMPERS, but many were due to dimensional issues.
As with any limit rule DO NOT DESIGN TO THE LIMIT. Give yourself a bit of margin to deal with variation in measurement technique, fabrication, and assembly stackup. This is speaking from designing and building a ROBOT that was less than 1/16" under a height limit for that year.