Cruise control 2nd and 3rd only

Been trying to get this functioning for some time... Wiring added from dash to existing correct clock spring and switches etc. clutch and brake already wired oem..

The car sits on 205/45x17 and initially had a petrol gearbox fitted in place of the 3.05 oem box. I fitted it as it was sold as a 1.6 tdci econetic box. I knew as soon as I drov it the gearing was lower. Anyway, drove it around for a bit, programmed the scm bcmii etc and the cruise light on the dash responds to selections from the buttons when in 2nd and 3rd above about 26mph or so..the other buttons all function, cancel, res etc...I altered the tyre size and circumference in the preselected box, saving the data and rebooting the module via forscan...all still the same.  In the meantime I had a bcmii misconfig error which apart from the MIL lamp didnt affect anything on the car. I assumed it was the box ratios contributing and just drove the car until I sourced another correct gearbox which I've just fitted.  I've been messing with the laptop and returned the asbuilt data to the bcmii ie the non cruise and std tyres/circumference.  This cleared the incompatibility error. Still the cruise functioned the same. I've just come back in from editing the tyres and circumference again and now have another incompatibile error on the PCM this time..I guess the PCM HEX needs adjusting but cant find any data on what a cruise parameter in the PCM ought to be...So, unless theres something else anyone can think of, how would I go about getting the correct code to enter at the correct place in the PCM ?  Guessing its not an easy ask.. 🤭 thanks for reading,

Dov