IMO the narrow diamond is not really suitable to play attacking mentality and I'd question how you would use mixed focus with no MR/ML or AMR/AML to attack down the flanks.
Playing against the wide diamond you may have more success like this.
----------DC--DC--DC--------------
---------------DMC------------------
ML---↓MC↓----MC----↓MC↓----MR
----------------ST
Use short passing through the middle with normal mentality pressing your own half. Zonal marking. NO O/S, No Force counter.
Or.
4-1-3-1-1/3Dc's-1-4-1-1/3-1-3-1-2 is good against the diamond tried and tested over four seasons.
-DL---DC---DC---DR
--------DMC
-ML-----MC------MR
--------AMC
---------ST
Same orders just change Focus to mixed as this can attack through both the centre and flanks and maybe mixed passing if you get really desperate.
If you need a goal or two, take off a DL/DR move the other three into DC's and add a striker or another MC, which ever you prefer, your MR/ML will still track his so you should have no problems as long as there not greyhounds.
Oh! and if you do remove a Defender take the arrows off the MC's.