There is no such thing as “perform meridian flip”. Not in Ekos and not in mounts. Mounts keep track of the hour angle and when 1) they have passed a certain value and 2) a goto to the current object is issued they will perform a meridian flip. If you want to perform a meridian flip then you can go to the mount tab and open the mount controls and click goto. If the mount doesn’t respond then it hasn’t passed its configured minimum hour angle yet.
The automatic meridian flip is working fine.
My problem is that, with my mount and telescope configuration, near zenith guiding works better when the telescope is on the east side pointing west. Guiding results are far better after the meridian flip. Just changing the counterweight-balance does not solve the issue. I believe, the mount's physical specifications would allow to flip 10-20° before reaching the meridian , so I probably could avoid the guiding issue if I could flip before the mount passes the meridian.
Yes, I was thinking about trying a negative value but it won't let me. I was wondering if setting HA>23hours would cause a meridian flip 15° before passing the meridian?
Even if you could somehow cheat EKOS to initiate a flip one hour before meridian, it would not work. All EKOS does is send a 'slew to target' command. The mount firmware then decides on which side that would be, EKOS has no influence on it. This is why the setting is limited to positive values, and even using zero can be dangerous in risking that the mount decides to stay where it is and not (yet) flip.....
The way that the Celestron mounts handle this is to have a pier side preference option. This can be Off, Prefer East, Prefer West and Prefer Current. They also have Ra limits which specify the range over which the preference works. ASCOM uses these to implement its set PierSide method.
If the OP has a Celestron GEM he could set his mount to Prefer East then a slew would cause the mount to flip up to 20 degrees early. EKOS can't currently set the flip hour angle any earlier than 0 but any normal slew would do so. (I may have east and west confused here.)
I can't say how other mounts handle this, in many cases they don't, but it may be worth digging into the detail of this in the mount information.
EQMod driver also has force pier side option which can be used to go to target on the "wrong" side of the meridian and do the flip early. I've used it quite frequently with HEQ5 and EQ8.