I do think EVA only upgrades during oversell situations and little to none based on fare class / IML status... They definitely op up much less than cx.

Flew TPE - SIN - TPE in elite last month. Plenty of seats available in Elite and RL. No op up (didn't expect it anyways).

And another TPE SIN segment In full fare economy this week. Economy was around 75% full and elite had less than 10 pax. (I'm IML gold). No op up haha.