Hey Peter
I have two Marlins and what works for me is having the front bead "sitting" on the top of the rear sight. Now that's not the way I was taught but seems to be the way I use the Marlin sights "naturally." Seems to hit pretty much where I point it, too.
ÇR
p.s. remember for CAS the white diamond needs to be blacked out--I used a magic marker to do the job on mine.