Ok, I got an answer that works for me 🙂
Im not a programmer but have been able to hack together a cura post processing plugin that seems to work fine for me.
I will attach it for anyone else should they experience the same issues.
Just drop it in the same folder as your cura post processing plugin scripts.
usual location
C:\Program Files\Ultimaker Cura 4.[xx.x] \plugins\PostProcessingPlugin\scripts
as a bonus it also makes my berdair more controllable, as it doesnt start turning until the S value is at least 26 and reaches max speed at 245'ish.
I can enter the berdairs start S value and Max S value and it now recalculates this as being the 0 - 100% fan range ansd also drops the decimal places by rounding
im also replacing any M107 with M106 S0