Leave that box unchecked. FTL modifiers aren't used for that specific [ie - '2'] keymap, they are only enabled on keymaps
such as FTL Assist Me, etc. The FTL will be used when the Assist keymap is called via 'Do Mapped Key.' As for why it isn't
working... well... I'm not sure.

I'm terribad at troubleshooting ISBoxer issues, and everything I have said above is going from memory.