Yaso1, welcome to FT.

Your question is sort of covered here.

But after talking with EK staff since that post, I've been told that upgrades are processed according to status, tier miles YTD (your year to date, not calendar year), and fare paid apparently comes into it.

I am sure there is some "system" or process to their often random method, but no one can really say for sure. It will differ from station to station and I am absolutely convinced its more to do with how oversold Y is rather than anything else.