My theory which is what I have learned from word of mouth, reading and direct observation is that the huge multi-sqauer mile flats off Poppy & Cotuit; all less than 10' dep tend to warm up first. Add the outflow of the bay's, add a warm sunny day, and water temp there is going to be 5 degrees or more warmer than the slightly deeper water around waquoit.
Its not that you can't find fish at waquoit or Falmouth; its just you'll find warmer water around Poppy.
You've boated the area enough; the flats around waquoit are perhaps 1/4 mile before the water is 15' deep; off Poppy and Cotuit you probably have to range out close to 1 to 1 1/2 mile to hit 10' deep.
Also look at a sat. photo of the area and notice the nice corner Poppy adn Cotuit form; kind of the end of a funnel.