I dont think the patio is a problem. Just because you have differing level of porosity in the sandstone, I dont think that is cause to think the patio has been constructed incorrectly.
I think your problem is porous face bricks used below DPC.
Im sure the ACOS will solve any patio issues, even if they dont solve the wet bricks below the dpc. If your bricks are porous there is nothing to stop them soaking up water as they are surrounded by soil from the surface downwards.
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