We don't have an SOP as such to cover this, but my normal drill is to input loadsheet %MAC in raw form, and then once level in the cruise at econ speed, look down at the trim indicator and input the figure from there. It seems to work, though it's only of consequence at high levels when considering a further climb or pondering buffet margins in choppy skies etc.
------------------
'Brighten my Northern Sky' Nick Drake R.I.P.