HELP!! No more adjustment on FF3

[wareagle22]

I was patterning my new Franchii Affinity 20 ga today and it started out shooting way low.  I kept moving the dot down to raise my POI until the FF3 bottomed out.  It's still shooting about 4" low and I'm stumped.  The FF3 is mounted on a Marlin 336 base and I took the protector off the sight and that helped me some but not near enough.  Anybody ever run into this and if so, what is the solution?  I've heard of guys shimming the rear of the sight to solve the problem but it just seems like something in my setup is wrong.  Any suggestions would be greatly appreciated. 

I'm shooting 1 5/8 oz TSS #9's

[turkey buster]

Sometimes just taking it off and remounting does the trick. You might not have it completely secured to the base

[Ruehter87]

Now that you know youve bottomed out the dot, try moving the dot way up and shoot a couple shots. Makes no sense I know, but try it.