Combined Fiberboard/Foam Traps

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In Sound on Sound's article here:

Room For Improvement

They say:

Because compressed Rockwool or glass fibre is denser than foam, it is more effective at low frequencies, but above a certain density is slightly less effective at high frequencies. It doesn't present such a visually attractive surface to the world as does foam, so we often face one panel of rockwool with one sheet of two-inch foam, and fix it into a frame with an air gap of a couple of inches behind it. This is an easy way to produce a cost-effective mid/high trap that looks professional and can be easily fixed to a wall or hung like a picture frame — and the foam counteracts the reduced HF absorption of the dense rockwool.

I was contemplating using 4" of 3PCF Knauf Ecose spaced 4" from the side walls (the "mirror reflection points" to the left and right of the mixing position) in the standard 2x4ft panels (one panel on each side). However, I also have 2x2ft Auralex foam panels that I was going to use for auxiliary purposes. Should I instead use 2" of the Ecose and 2" of foam? Would this be more effective at dampening a broader acoustic range?