No it's not for bigging up purposes. The largest single henge is Durrington - 500m and is certainly a whopper, yet Thornborough, if seen as a single site - based on identical build dates etc. represents a larger ritual space for a single ritual event. I know that a lot of this is debateable, but to my mind, in the balance of probability - Thornborough was set up from the outset to be Britains largest ritual site, part of Britains largest ritual landscape. It appears to have maintained that position for a significant length of time and it's unique linear alignment with the other monuments in the area makes the site stand out as being highly unique.