FLX S48 Effect Parameters

[Rye]

Hey, I've been trying to solve this problem for a while - I've checked as many different forums posts as I could find to no avail. 

I'm using an FLX S48 console, with a bunch of different Tungsten and LED lights for a venue I work at. 

The end result I'm hoping for is a playback fader that can fade a rainbow colour effect in and out over the top of various other colours. 

For instance, I'll have a Blue wash on stage, and I want to fade that into a blue tinted rainbow effect, and then keep the moving colour effect but change the tint to red or green or whatever colour. 

I've tried a bunch of different methods with mixed results, but finally managed to get something close to what I wanted. 

I have some Playbacks with various colours - and then what I've been calling my Rainbow Fader. On this fader I've saved every LED with a Rainbow Effect at the speed/offset I want, but not recording the intensity; and with the colour values set to 0/ignored instead of the default 127. I've also set the fader to control Effect. 

Now, when I have the Rainbow Fader up, then fade in another colour like blue on a different playback, it fades into a nice blue-ish rainbow effect. Very nice, was what I was hoping for. 

The slight problem is doing it the other way around. If I have the colour up already and fade in the Rainbow Fader, it does indeed fade into the effect - but it also fades in the recorded Effect Speed, meaning if I fade it up fast, the colours rapidly shift around all over the place as it alters the effect speed really fast until it reached the recorded value. 

I've sort of been able to work around this by putting in a Raise/Lower time of like, 5 seconds. It helps smooth the effect speed transition, but is a bit limiting. 

What I was hoping for was to be able to control the Effect Size on the fader, but keep the Effect Speed the same the whole time. 

I've tried using stuff like the Speed Override, but either I'm not doing it correctly or it doesn't seem to work. 

I thought it would work like controlling the individual colour values on playback faders - where you can select/de-select the RGB values before recording, just with the Effect Parameters instead (Intensity, Speed, Size, Offset) 

I can also imagine other scenarios where this could be useful - maybe you have a moving head effect where you want the size to stay consistent - but be able to control the speed on a fader. Or maybe you want the speed/size to stay the same and control the offset on a fader. 

Would anyone know if there's a way of achieving something like the effect I'm hoping for, or perhaps a way of doing something like I described? Any helps would be appreciated. 

Thanks