It looks like I didn't understand your question.

Telltales a useful tool, but not the complete story. It's like when your calculator tell you, that you have $352.4599999999... in the bank.

First, you have to know what they are saying. For example, with the crew over sheeting the jib, the main about right and sailing at about the right angle, I know what they look like on my boat. To find out what they look like on your boat practice a little. Fall off a little, trim the sails and see what things look like. Pinch a little and do the same. Is there a difference that depends on the course and not how the sails are trimmed? Now with the sails fixed, fall off and head up. See what this does to the tell tales and the feel of the boat. Now do this in every possible wind speed (This might take a couple of years). Get in the habit of running through a short version between races so you will know what they are supposed to look like.

Flowing straight is not always fastest. My boat and sails go upwind best with the top telltales fluttering a little less than half the time. This is not uncommon.

Light air sailing is an art that requires experience. I learned fun sailing on a lake. If I couldn't sail back, I had to paddle. When the wind is really light I set the main using where the taper goes into the mainsheet and then use a feather wind indicator to steer the boat

A lot of this is experience. Try and remember what works and what doesn't and avoid what doesn't work.