Here in Aus, things appear fairly logical. One generally pays for the berth based on size of the berth. Some marinas have them down to 9/10metres, but 11 in the general minimum, and good for boats up to 36'. I own one of them for my 34'er, but it's 36' if one is pedantic re anchor pulpit and swim-step, (or duckboard as we tend to call them). However, it would be stupid waste for my boat to take up a 12m berth.
From 11m they tend to go to 12m, which suits boats to ~38-42', then they usually jump to about 14-15m, for 50-55'ers, etc, as people here don't froth at the mouth over a wee bit of overhang, after all it's only occupying air space, so as long as it does not constitute a danger to folk walking the dock, no worries mate. Some folk lower their anchor a tad to minimise this risk if the moor bow in and the anchor protrudes a bit.
Any bigger than ~ 55' usually means paying for two, end to end berths at the end of the finger, although some marinas do have up to 20m berths.
Personally, I feel making a fuss and charging extra for literal length also taking in projections that are so variable, and as several have mentioned, can be added or subtracted merely by folding up, changing only air space occupied but not the amount of usable berth they take up, is fairly dubious as a way of valuing space taken. What really dictates how much marina real estate they occupy, which in my view is what it is fair to charge for, is what 'minimum berth length' they realistically need to effectively and securely moor, and with practical access to the vessel. and without interfering with other boat traffic. After all, the marina developers paid for the land adjoining and the installed structures, not the water surrounding it.