Easily Explained by the "Flat Plate Effect"
Picky
Assume that, after some extremes of towards or away from sun exposure). a largish segment of a launch-shattered RCC section departed the leading edge in orbit during a mild manoeuvre i.e. this being what eems to have been logged on radar. Upon re-entry the remaining segments of that RCC section would have rapidly heated up, oxidized and were seen detaching brightly in the pre-dawn darkness as the Orbiter crossed California. This progressively laid bare the inconel alloy support brackets and the flat plate of the aluminium leading edge. Hypersonic shocks and flat plates aren't an area of intense study because like water and oil the two aren't really compatible. But what we do know from the photo taken about a minute before the breakup is that the super-heated plasma generated by an oblique flat-plate is many times magnitude hotter than anything before seen on re-entry (to quote a NASA investigator). That was seen on the photo as a projection ahead of the left inboard wing. Until such time as all/most of the RCC was gone from that section, or until the Mach No maximized, the resulting forward projecting plasma bubble probably fell short of the supply water dump nozzle. As the oblique aluminium leading edge became TOTALLY exposed to the hypersonic flow, the bubble would have gradually grown and projected further forward, affecting the SWDN temperatures. Clear so far?
However, how to explain the later reduction of that SWDN temperature? Easy. As the unzippering effect laid bare more and more oblique flat-plate leading edge outboard (i.e. as their RCC sections detached due to oxidization and their inconel brackets heat-eroding ), that forward projecting super-heated plasma bubble would have changed shape, fallen back and become more uniform span-wise. Think of it as holding your finger over a garden hose to achieve max range - and then later changing the spray pattern to a closer-in area coverage by changing the nozzle choke. Furthermore, the initial forward-projected plasma bubble resulting from a single lost RCC section would have been deflected inwards (towards the orbiter nose) by the intact RCC section outboard and alongside of it (i.e. next along outboard), until it too was eaten away by the superheated plasma.
Eventually, as the Mach Number dropped, the shocks would have also decreased in their forward projected size and temperature (although this would also have been a function of the loss of focussing by intact outboard RCC sections - as the damage ate RCC LE further and further outboard.
To me it seems a clear vindication, justification, verification, confirmation of the flat-plate theory of unintentionally generated destructive super-heated plasma - and tends to confirm what was first theorized based upon the USAF photo.