I often model plastic parts, and a common problem I have is getting a fillet to end correctly at a parting line. I really want it to end at the parting plane, but the easy standard fillet tool often pushes past or pulls short of the correct plane, so I've had to go through a lot of extra work to get it right.
I find by adding a tiny bit of geometry beforehand, the fillet will end correctly. The extra geometry gets consumed by the fillet, so it's a fairly painless workaround, at least compared to other stuff I have tried.
The images below show the story (I hope).
WIthout the extra move: