I like your approach.

My protocol is:

1.) Stop at red light being the second car in the row

2.) Casually rest thumb on horn button

3.) Vibe till traffic stops, observe vehicle up front for breaklights going off, any movement or judder signaling the driver is getting ready, on/off system restarts the engine, etc.

4.) If any effort is observed: feel content and have faith in my fellow man

If no effort is observed: as soon as the light turns green, flash once, observe response for 1 second. If no effect, lay on the horn until vehicle starts moving. Overtake at next opportunity, because there are a lot of lights and ahead and this is a clearly distracted driver, so keep distance.