A thorough search of many forums on the net shows Meade f6.3 reducer spacings to be anywhere between 85mm to 105mm, i was using 105mm thinking that was OK as it was the most common spacing suggested, so which spacing is right for my setup.
I decided to use the bintel astronomy calculator to find the correct arcsec/pixel using a 12inch Meade LX200 with f6.3 reducer and a ZWO ASI070MC pro at bin2x2.
https://www.bintel.com.au/tools/astronomy-calculator
The result was 1.03 arcsec/pixel for
1920.24 f6.3 at bin2x2
Now all that was needed was to image at various f6.3 reducer Spacings to find which spacing produced 1.03 arcsec/pixel by uploading the image for plate solving.
https://nova.astrometry.net/upload
Results:
105mm = 1.18 arcsec/pixel
100mm = 1.14 arcsec/pixel
90mm = 1.07 arcsec/pixel
85mm = 1.03 arcsec/pixel
The 85mm spacing produced 1.03 arcsec/pixel, this should be the optimal setting, i will image using this spacing in the future and see if it improves my images.