If lift and control authority derive from Indicated Air speed (IAS), why do energy-maneuvering (EM) diagrams use True Air Speed (TAS) as their x axis?

Question

Example EM diagram for P-51D and Spitfire MkIX: https://ww2aircraft.net/forum/attachments/areas-gif.594279/

Why is the X axis given in TAS rather than IAS? From my understanding, how much lift a given airframe experiences is correlated to IAS rather than TAS and lift directly correlates to turn performance (higher lift-weight ratio at a given bank angle and G, the better the turn performance). Likewise, by my understanding elevator authority is based upon IAS for compression and minimums.

So, assuming my understanding is correct, why do we use TAS?

In: Physics

Answer 1

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