Motorhome height and booking online

Just been going through the internet to get best deal for our first trip to France. Although heading for the Loire decided to take the Dover crossing because it is so much cheaper. Was originally looking at Speedferries because of their prices but they do have the 2.0m width limit (including mirrors) which I hear they rigedly enforce, also could not get the £88 deal, was going to be £102 and limited times, basically they are fully booked.
So after using a couple of search engines ended up at Smartferries (Leisure Drive) and they came back with a price of £98 on P&O in June, however there is a height limit of 2.5m for online booking, surprising since they do list Motorhome as an option, so ended up having to call them, they came back to me an hour later with the same price. Looking at a few other sites many seem to have this height restriction, and with an AS Duetto ours isn't exactly big. Anyone else come across this ?