It sounds like you're on the right track,
If you plot the power required vs indicated airspeed on a graph, you will see a "bucket" shape, with the power required rising on both sides. On the slow side, as the power required increases (to fly more slowly), you are in the zone referred to as "behind the power curve".
The best endurance speed will be about where a line from the origin of the graph (0,0) intersects the line you have drawn. I did this exactly for my C150 many years ago, and found that 2100 RPM is the best endurance power setting, and 1900 RPM is the minimum power required to mantain level flight.
You will probably find the graphs midway down this
Propeller Aircraft Performance and The Bootstrap Approach: Formulas and Graphs page informative.
There is lots of printed information on this subject, and I can recommend so reading if you like. I'm sure that you'll get many other answers from very well informed aviators here as well.
Welcome to PPRuNe, Pilot DAR