To the OP subject, when I fly sparse in my 10g round igloo cooler, I just leave about 1-2 inches of liquid on top of the mash and then put a chunk of silicone hose from the HLT around the perimeter about 3/4 of a turn sitting right on the grain. This is injecting tangentially (and horizontally) from the HLT. When it is running, the liquid has a slow rotation to it as the sparge water comes in. No manifolds or arms or whatever, just 4' of 1/2 inch hose.
Sometimes I just run all the sparge water into the cooler at once after the liquid has drained to the level of the grain bed. That way I don't worry about rates, but it could end up compressing the mash I suppose ( not that it has ever happened to me).