I never studied it for North American racing because there is so much more useful data to go by. All the normal RDSS/Sartin factors are absent for Foreign horses with no internal time segments and beaten-length SO, those horses can be undervalued. And, only the best horses would be sent to the US from Europe/UK/Ireland so they're not exactly 'plodders', though they are mysteries.
It's an interesting investigation though. My sense is that it would not be an impactful factor. You could give it a go
Ted