Presumably that was caused by turbulence inside the scope rather than distortion of the scope body, in which case magnesium and aluminium alloy bodies would not be much better than polycarbonate.
I fear that my green 883 would absorb almost as much IR as a black one. I dont like socs but perhaps this is a valid justification for them.
Back then, both I and Jan Meijerink conducted some further testing with other scopes also, some with metal bodies (Nikon Fieldscope) and some with polycarbonate (Kowa 823) and using a hot water bottle/timer as a repeatable heat source. The metal bodied scopes had significantly less (almost none) image degradation from unsymmetrically applied heat. Whether it is dimensional distortion or turbulence I'm not sure, but since polycarbonate has much lower heat conductivity, when sun shines or a heat pad applies heat to one side of a scope only, there was very obvious temperature difference between the heated and unheated sides, whereas with metal bodied scopes very little.