Selecting mass floors in the selected mass

I have been using the MassFloor.Mass from the Clockwork package with great success.
For reasons of how other staff would use the script, I need to do the opposite - getting the mass floors in a selected mass. This should be a simple process but I am unable to find the right nodes.

I could select all mass floors and filter out by whether they match the mass selected, but that seems to be a very round about way to just get the floors in the mass.

Am I missing something?
Thanks in advance!