I couldn’t work out why the z-axis flex coupler hadn’t helped really improved my z-wobble issues. Eventually I realised that I had stopped it flexing by having the motor shaft and the lead screw butted up against one another when I tightened up the flex coupler. So, if you are like me and have a flex coupler that has holes that go all the way through, then please make sure you raise the lead screw top mount so that there is a gap between them before tightening it up.
Don’t put them too far apart though. You might end up with more wobble than what you are trying to cure.