Keeping on the slope (3°, by the way, not 4°!)
A closer study of what he said was that four degrees is for light singles. In fact, a powered approach in a Cessna 150 with 1200 rpm and full flap is more like six degree angle with a glide approach in a Tiger Moth (no flaps)at idle throttle about the same. Mr Jacobson's theory on flare technique was designed to be applicable to jet transports as well as lighties and nothing to do with the actual angle of approach. Three degrees is purely an ILS angle and used by heavier types.