Waren9,
You're confusing power with thrust curves in a *piston*. In a piston engine fuel flow is approx. proportional to power unlike a jet where FF is approx. proportional to thrust so endurance matches the lowest drag point & range the drag tangent
For a piston engine aircraft max. endurance occurs at minimum *power* required. Best range occurs at the tangent to the power curve, which also correlates to Min. Drag, best L/D ratio and best range glide speed/Vg