Issue with OffsetSrf of a Variable radius fillet going to radius 0. How to create something like this?

Hi everyone,
After several tries i relized that probably the best thing to do was to ask for help.
The final goal is to create a metal box composed by three cointainers which are filleted together.
The box has to end straight, that’s why I used the variable fillet command for surfaces.
The moment I offset the surface, things happens.
Any tips, suggestions on how to avoid this problems?
Anything is really appreciated!

Here’s the file: VariableRadiusFillet_issue.3dm (17.2 MB)

Hello - I think I’d leave the tapered fillets out, offset, then add the fillets to both sets of edges.