For large horses, I know, when you measure the canon....say 16"......just use the same number and convert to hands. So, a 16" canon, will be a 16 Hand horse. And remember, these are just averages.
I personally have never measured anything but foals up to 4 months old to judge adult height, but it sounds like your measurements are proving the HH table correct. 9.5" being a 9.5 hand horse, or 38". That's fun to know!