This indicates watching the inside telltale going upwind.

Not sure which page you are talking about when you say "this indicates..." but in anycase, since you are dealing with lift, you are more concerned about the outside tell tales being smooth.

From my experience going upwind, if my inside telltale begins to flutter I see a definite decrease in boat speed,but if the outside telltale flutters much less so. But I would agree that they were equally important. I love the sensation when you turn off the wind just enough for the inside telltale to lay flat, the boat heels a bit more, and you feel the power of the wind as you settle into what we call 'the groove'. As your friend pointed out, it is like 'seeing the wind', and the force is with you. Thank you.

In another regard, since the pressure on the helm will be to weather going upwind, the helmsman must watch the inside telltale to counteract any sign of flutter.