A dollars-per-square-foot-per-year commission is linear in both size and term. Lengthen the deal and the check grows; shrink the footprint and it shrinks. A percent-of-aggregate-rent model couples the commission to face rate and escalations instead — which is a different economic object.
A worked stub
25,000 SF, ten-year term, $1.50/SF/year: commission is $1.50 × 25,000 × 10 = $375,000. Independent of whether the starting rent is $30 or $34. Put the same deal through a 4% of face-rent engine and the commission now rides the rent roll, including escalations you have not even negotiated yet.
If your ranking of three River North options uses the wrong object, you will pick the wrong building. Not because the NER formula is hard — because the commission line was translated instead of entered as written.