Scotts Edgeguard Setting for 21-0-0

Can anyone answer this? I bought a bag of 21-0-0 and want to apply 1 lb/1K sq ft of nitrogen using a Scotts edgeguard spreader. If I'm doing the math right, I believe I need 4.76 lbs of product to get 1 lb / 1 K (1 lb ÷ 0.21 = 4.76)

When using Milorganite, the bag says to put 8lbs/500 sq ft (so 16 lbs per 1K) and the setting on the edgeguard is 11.5.

So my question is, since the 21-0-0 is about the same granular size as milorganite, can I simply divide the setting by 1/3 (since I need approximately 1/3 of the nitrogen as compared to the milorganite). If I use round numbers (12 ÷ 3 = 4) that's the setting I come up with.

I guess I could weigh out 5 lbs of the nitrogen and measure out a 1K sq ft section of yard and mess with the settings that way, but I was hoping someone may have the answer already.

Or maybe I'm over thinking it and I should just set it on 4 and do a double pass and see how the grass responds. This is what I have already done this on the front lawn, but now I'm second guessing it.