Whether you are choosing momentary or continuous mode, you are picking, with TT Pro series collars (Flyway included) a RANGE with your dial setting. Then you have instantaneous capability to go up and down the range with immediate choices, that take away the need to lose time or focus by having to turn a knob.
I am NOT touching my ear or zapping myself today. But just for the heck of it, I'm using my Pro 500 and listening to the sound at the prongs.
A 4 high continuous is a pretty loud, higher pitched, rapidly pulsing sound that is easy to hear. A 5 low is a much lower pitched clackety sounding slower pulse. It makes sense just to the sound that a 4 high is going to stimulate the dog much more than a 5 low.
Try it - no pain or test lights needed. P.S. Don't touch your ear to the contacts!