sleeper-less subfloor over slab?

I'm converting a garage to habitable space. It's bone-dry, but I'll be adding a supplemental barrier on top of the slab.
http://www.apawood.org/pdfs/managed/TT-007_Concslab.pdf describes a method of wood subfloor over foam over concrete instead of the more common subfloor attched to sleepers over concrete.
I need to keep my whole floor (insulation, sub, carpet & pad) under 2" so the ceiling height will be 7'6" when it's insulated. I could use 1" foam and 2x sleepers ripped to only 1", but what about skipping the sleepers altogether?
Dow's page on polystyrene and polyisocyanurate insulation doesn't mention this application. My guess is that the tougher polyiso is a good idea for crush-resistance.
There are UK and Australia web pages that mention this technique, but the APA page is the only US one I've seen. Probably going to be hard to get the inspector to OK this. It's also more work for the subfloor- I can't get 4-edge tongue & groove, so I'll have to use splice plates.
Would my idea of 1" sleepers with 1" insulation work or is the 1/2" gap when using 2x sleepers required for some reason?
Thanks in advance!
-Morgan
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A method sometimes used for hardwood over radiant floors is two layers of 1/2' ply (4 x 4) glued and screwed, floated over foam.
MH

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