(This question has been edited to reflect a change in perspective: based on answers to the related question What is causing these "corners" on this F-104 V-n diagram?, I now believe that the curves on the upper left edge of the envelope are intended to represent the stall speed throughout their entirety, both above and below the distinct "corners". If the aircraft is being limited by something other than the actual stall along some portions of these curves, then it would be helpful to clarify and explain that in an answer either to the present question or the one linked above.)
In this V-n diagram for an F-104 (source: this Wikipedia link), why does the stall speed at any given G-loading (in terms of IAS) decrease with altitude-- at least in the part of the envelope that is below the sharp "corners"?
And why is the opposite is true for data points above the "corners"?
For example-- (numbers are approximate)--
Below the "corners"--
20,000', 5G, 415 knots IAS, versus 30,000', 5G, 375 knots IAS
30,000', 3G, 330 knots IAS, versus 40,000', 3G, 295 knots IAS
60,000', 1G, 175 knots IAS, versus 70,000', 1G, 140 knots IAS
Above the "corners"--
30,000', 5G, 375 knots IAS, versus 40,000', 5G, 475 knots IAS
And why do the curves cross each other?
(For example, at about 350 KIAS and 3.5G, the 40,000' curve crosses the 30,000' curve.)
Related ASE questions and answers-- but some of which seem to suggest the opposite relationship should be the case (at least for the "below the corners" cases)--
Why does indicated stall speed change? (see question and all answers)
What causes a slight increases in indicated stall speed with altitude? (see question and all answers)
How does the IAS stall speed vary with increasing altitude? (see question and all answers)