On broad reaches tell tales don't do much anyway. Once the apparent wind is abaft the beam the sails aren't really giving much lift, they are pulling the boat. From a beam reach and higher the telltales tell all about sail shape.
There is a tide in the affairs of men,
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
Shakespeare, Julius Caesar IV, iii, 217