That works, but has nothing to do with Stand-In switches. It's intended for use with an expression pedal, hence the "heel down" part. That said, a closed switch is effectively the same as an expression pedal at heel down since the tip and sleeve connectors are basically shorted together at that point.
I think some folks mistakenly use "Stand-In Switch" to refer to any external switch, and that adds to the confusion. Stand-In switches are just one possible use for external switches via the FC Controllers menu. External switches can also be assigned directly to other functions such as modifier sources or in the MIDI/Remote menu as you've done above. In other words, not all external switches are Stand-In switches. Not trying to split hairs, but rather offer some clarification so others don't have the same confusion.