870 FF3 mounting question

[bdgsc]

can y'all give me some feedback about d and t mounting an ff3 on an 870. is there any particular spot on the receiver thats best? or is it preference/aesthetics? using the 336 mount. thanks.

[SumToy]

We put them on the back.   It is thicker. 

[bdgsc]

ok cool. thanks. i found the thread where u put this pic. can u ballpark the red arrow?

[SumToy]

that was just set on the gun to show.  You can move it on back if you want.