The only authority I really have is to present exactly what the EPA now requires on all labels of all pyrethroids, and for liquid applications it now states this - "Other than applications to building foundations, all outdoor applications to impervious surfaces such as sidewalks, driveways, patios, porches and structural surfaces (such as windows, doors, and eaves) are limited to spot and crack-and-crevice applications, only."

What you are asking is that gray area between some solid expanse such as a patio and an expanse covered by something like coarse gravel, where an application would seem still to be allowed since the spray will quickly move through that gravel and to the soil, where it is able to soak in rather than run off with rain or irrigation. So, would it still be okay to spray over, let's say, river rocks 1 inch in diameter? How about river rocks 6 inches in diameter, or flagstone 2 feet wide. Obviously any liquid that runs off those rocks goes immediately to the soil below even though the rocks themselves clearly are "impervious". How about a patio of 1 foot wide paving blocks with 1/4 inch gap of sand or soil between them? Now we could be getting to the point where there might not be enough gap to allow all the liquid to flow in before some of it flows off and heads to the gutter. 

It is this gradation that worries me enough to avoid making a firm statement on this, and it is important for your regulatory agency to be given the opportunity to address it instead. If it is left up to every technician to make his own judgment call we likely would have some technicians deciding that ANY covering that has at least some gaps round edges would be sufficient to allow the spray, when soaked by a heavy rain, to flow down to the soil, and this doesn't seem reasonable.