I think the Wix guy was doing a CYA thing, or just does not have enough experience with non-standard filter mounts and external oil coolers. Did he give you are reason or give you a pressure drop numbers to work with? I've gone through this all and come up with the pressure drop numbers... with 1/2" ID lines, you would be hard pressed to get more than 1 psi drop. You'll get more drop in a hard 90 with the stock internal oil passage bores. And the point of lines to oil coolers being long is just another indicator of it being OK. I've done this over and over and have not had any pressure drop that ever showed up on a gauge.
And, the large remote filter with the large filter will provide cooling of the oil. Putting the small filter under the headers won't cool the oil and might possible add heat to the oil, especially with the black Wix filter casing absorbing radiant heat.
But ether way, I hope you get the results you want.