Kampa Motor Rally Air Awning Heights

Rescuerabbit2

We have an Autotrail Apache 634 and would like to buy a Kampa awning, having measured the height of the awning track to the floor we find this to be 262 depending on the levelness of the ground, which of course it never truly is. Has anyone got a Kampa awning which they use on a 634 and if so is it a large or an extra large please. Have asked the retailer who are a bit unsure as we are so near the difference in height between the two.