An exception is the B-Wing model that used a known 1/32 scale figure that was converted (simple head-swap) and fit within a fully detailed cockpit, which establishes a stronger case for 1/32 being the scale of that model. However, for the TIE especially, the figure was not intended to be 'seen' and really only blocks the view of the armature.
So where would the scale being set 1/24 come from? It is actually an arbitrary value since scale was not important to the use/function of the studio filming miniatures.
Exactly
Studio Scale plays a bit loose with things and they are made as large as needed for a good looking filming model rather than adhering to any set scale. Sure they keep things in the ballpark, but also fudge things as needed
Take the A-Wing for example. there was this pilot (which makes the A-Wing a much larger ship if you scale from the pilot)
But then they also had an A-Wing with this way oversized pilot (had to wind up cutting the legs off to fit) which makes the ship a drastically smaller scale. THis pilot got used because it's head could be puppeteered and looked good on camera
IIRC the original Studio Scale Tie Fighters according to some article early on were built as 1/16 scale models. But I think they wound up putting 1/24 figures in them as it was "close enough" Likewise with the A-Wing, they had two different pilot figures. One was a much smaller figure
that is why the Bandai B-Wing pilot is so small for 1/72.
They kept the pilot proportional in size to fit the cockpit, but the whole scale went under the assumption of a 1/24 scale studio model. This resulted in a pilot figure that is really more like 1/80 or even as small as HO scale.
Same for the Bandai A-Wing, but going the other way. The pilot figure was kept proportional, but since the ship scale was changed, that made the pilot figure have to be a larger scale that is closer to 1/60 or so to remain proportional
I really wish they had done the opposite and scaled things from a 1/72 pilot in a truly proportional 1/72 cockpit