On the subject of fretboard radius:
Both Gibson and Heritage guitars are usually specified as "12" radius".
However, it is not at all unusual to find upon measuring the actual instrument in your hand to be anywhere from 9.5" to 14" radius!!!
My 2001 H535, with all the factory nibs in place (meaning it absolutely left the factory this way) had a 10.5" fretboard radius.
I've seen plenty of Gibson guitars, going all the way back to the 1950's, which had fretboard radius well smaller than the spec-sheet number of 12".
Usually, radius doesn't matter that much, but if does matter as in the OP's situation trying to fit a 12-string capo, it would be important to actually measure it than to go by the spec sheet.
On the 12-string capo, I really like the G7th Capo with the 12-string option. It works really well on acoustic 12-strings and electrics with the normal order of octave strings. (octave above the root string). Many electrics, and some acoustics (like the Taylor 652CE 12-string) have the octave courses reversed. One of the reasons I quickly decided the Taylor was not for me.