Sorry for the slow response, been travelling.
Yes, the range has a Workbook scope.
But I just figured out the issue. That cell named XLSLIM_RUN_AT_START contains this formula using two named references to cells containing the paths to my .py module file and my python environment.
=RegisterPyModule(module,python)
The xlslim-addin.log says that xlSlim calculated this XLSLIM_RUN_AT_START cell. However, the UDFs from the Python module are not recognized until I manually run the cell again. So I'm not sure if it actually calculates this cell or not.
The workaround is to replace the "module" and "python" names in RegisterPyModule() with direct references to input cells (B4 and B5 in my case),. Then the formula in XLSLIM_RUN_AT_START does indeed execute properly and the imported functions are updated.
Also, powertip for anyone on Windows who needs to monitor the changes to a log file in real time this PowerShell command is useful:
get-content 'C:\Users\<username>\AppData\Roaming\Microsoft\AddIns\xlSlim\xlslim-addin.log' -Tail 0 -Wait