A form based code has usually some numbers behind, explaining the formal result. The following images show how the same floor-area ratio can have different consequences in formal terms.

As a begining: 20 lots, 10 for each street frontage, with 6×25 m (150 sq m), a common real estate product (at least in Europe). The sidewalk is not counted on these calculations, having considered it is a part of the public right of way.

A floor area ratio of 1 would mean covering the whole lot with 1 level

If half that surface is put on top of the other half, gardens appear. Still 20 homes with 150 sq m of built-up area, but much better as there can be windows…

If lots have twice the lot line length (12×25 m, 300 sq m lots), you reduce the number of homes by half, each with 300 sq m as built up area. Open space is on the lateral setbacks, but it is not necesarily attractive…

If lots become 20×25 m, with a floor area of 500 sq m, you get just 6 lots, and each home, with 500 sq m of built up area, is in the center of its garden… but 500 sq m are a bit too much for such lots, or it is perharps better to think about multifamily housing (each floor has 250 sq m).

The same layout with 500 sq m lots can become quite different with 4 floors, each with 125 sq m, so  two appartments can fit inside. 48 homes on the same land initially subdivided for 20…