So when they process op-up, will they give priority over SL or EM first? I have both SL and EM and deciding which one should I use for OLCI.

In the past I always thought that EM should give you better chance and I consistently get op-up from Y to PY on BKK-HKG-JPN routes. But one time after I got op-upped I ask to change my FF from EM to SL at BKK check-in counter and the agent said he need to call and ask if I will still eligible for op-up, before he told my that his supervisor said SL priority is over EM so I should keep the upgraded seat.

So anyone has experience or any idea regard SL/EM thing? Thank you.