Indeed it is - but,as you imply, that's for the lazy. I suspect that, if one can be bothered to do the calculations, 10mm² will usually be adequate. It can't be less than 10mm², since there is also a requirement for its CSA to be at least that required for PMB - which, with PME, is a minimum of 10mm² (unless otherwise dictated by DNO!).
Kind Regards, John.
