scroll down the page a little and you'll see a section specifically stating that cable losses should be less than 1%, and a diagram showing the volt drop for different lengths of different CSA cables, which I referenced earlier.GAVIN A ....are you saying that you would ignore the manufacturers instructions and install 2.5mm cable because you did some calculations !!
OK so the diagram is for the 3300TL, but as I said, that's more appropriate here anyway as the system isn't going to be outputing significantly more than the panels rated output very often / at all.
Not that we'd be using 2.5mm2, I'm just pointing out that it's not dangerous to do so, and looks to be somewhere in the region of within manufacturers recommendations and below the 1% max volt drop MCS recommend. Certainly too close for me to want to call it so definitely over the internet as being undersized.