Advice on fitting mid-ships cleats

Does anyone have experience fitting mid-ships cleats? JR advised placing above saloon recess but this seems too far forward - so advice on position.

The underside of the deck has a ridge in the construction so that the backing plate JR recommends has to be just the right size so as not to be across the ridge - so advice on backing plate welcomed.

Registration of cleat bolts and backing plate might be problematic to ensure in practice - any advice?

How thick is the deck?

Thanks for any advice

Yes we bought a Barton genoa track cleat at great expense - only to find that it doesn't clear the heads of the screws attaching the track to the deck.

Try before you buy!

I would only use the midship cleat long enough to get the bow and stern lines on when single handed. I would use them for springs even though the loads are much more lateral.

For a temporary hold when coming alongside single handed I run a piece of 10mm three strand out through the spinnaker pole deck mounting - it has lot's of bolts and likely stronger that the nylon anyway. 

I think mine are even further forward than JR suggests, I cant remember why but they still work. They may even be between the caps and aft lowers.
From dodgy memory the deck is c1/4in but much thicker near the join - so, as you imply, you will need to epoxy or glass a block in to level things out. I then used a substantial stainless plate. Above decks I used teak blocks to raise the cleat near to the level of the bulwarks and didn't fit fairleads, though you can fit brass rubbing strips if it proves a problem.
Cast aluminium 4 bolt cleats will match the existing and are possibly more useful than the small items you sometimes see.
Like the others I often use a device attached to the genoa track, Barton do a turning block that is fairly cheap and can be made to fit.

Let us know if you intend to go ahead and I will take some snaps.