By larger core, I meant deeper or thicker core. RS4, IPP, AWE or other side mount intercoolers have one limiting factor: frontal area. It is nearly identical for all of them. And we all know how frontal area is critical for cooling. So, by keeping this variable constant and increasing the volume by making IC deeper, perhaps is not the best way to increase IC efficiency.
I fully agree that height, width, depth, fin count, tube type, interior construction, etc...all important factors, thus I mentioned "fine balance" in my original post.