In the US you encounter the same thing. You are "shopping" for a site and the system quizzes you on your rig, length number of slides, etc, then uses that info to show you sites. These sites are rarely measured accurately. Put in minimal info and make the system show you all available sites, or go thru the drill of inputting the correct info, then you can switch to "available sites" further on and look at all of them.
The different systems are a confusing mess, some are downright difficult to use, some are easy.
A few parks do not allow you to overhang the gravel/pavement of the pad, most do not care, some have trees in the way, so you are limited on the overhang.
Charles