So after nailing all those sleepers down, I found out almost instantly that they were not holding.
New Sleepers for Sand Thermal Mass Radiant Floor
Sleepers on Styrofoam – Thermal mass radiant floor
So the bedrooms are going to have wood floors, specifically nail down wood floors. Therefore concrete is not an option as I can’t nail into it. So the method I choose was to lay out sleepers to support the floor