I can find no fault with the study you posted, HOWEVER- they use an example for "heavy clay" of .2" per hour hydraulic conductivity.   The subsoil perc rates on some of the types we are working with are .03-.06" per hour.   Not knocking what you are doing if it works for your location at all, but those are the reasons why a generic spacing/size/depth recommendation doesn't apply equally everywhere.   And it's why a bunch of 3" pipe, shallower and at maybe 1/2 or 1/3 the spacing of what was typical installation certainly before widespread yield monitors in combines, has become more standard "here".