You are correct, that’s exactly how it works. It depends on your BPM, since it is 256 times per beat. So kinda “wonky” and unintuitive, yes, but completely predictable and perfectly precise. So if you know it’s limitations and don’t push past those, it is exactly WYSIWYG.
Check the above thread for more info. I also learned a thing here and shouldn’t have written anything before checking the facts.
You can work around this problem by rendering your drums to samples, and therefore removing any changes to the envelope timing when changing the tempo.