Honestly - it never even came to mind that the splat ruler needed to cover shimmiers too.
I don't think there's an issue with the physics itself. Climbers simply get closer to the ceiling than shimmiers do, that makes sense; one is bumping his head, one is hanging by his arms. I doubt that it was specifically outright intended by Nepster (who implemented the Shimmier) that it should have a slightly lower fall start, but I certainly don't believe it's a problem.
My train of thought here went "shit, the ruler needs to cover the shimmier too", then "no, that's going to make it too messy, perhaps seperate rulers are needed", then "this would need to be different hotkeys, so should be configured as a single key with multiple sub-settings similar to Select Skill etc" which ultimately lead me to: Should helpers like the splat ruler be fully user-customizable, with some reasonable defaults - which could include "plain fall ruler", "climber fall ruler" and "shimmier fall ruler" - provided with NL?
If multiple options, with such a setup, were to be implemented, becoming user-customizable would almost happen just as a side effect of handling the easiest way to allow adding new ones in the future.
This is something I need to follow up on as a seperate idea. But as far as the original issue here is - no bug.