Well Chris,
You can check your parameter through the CUI. With groups only text parameters are allowed to have this setting. The interesting parameters with values can't be used. THe only one I found and sometimes use as a boolean is a currency parameter. But length, area ect. parameters, forget it.
I mailed it to Adesk support some time ago and the gave an explanation that parameters like length and area, could make a family instable and that's why they restricted it to mostly textparameters.
