Just put 3 or 4 in and put less water in to compensate for the ice. Sorry I cant be much more help I dont actually measure mine. I get a pint glass put about 1/4 crushed ice make it upto half pint just over and chuck it into smoothie mixer powder in an it always comes out nice and thick an cold.
i do 3 ice cubes crushed and with about 200ml of water i think it is just finding it the exact way you like it but i love it like this as it doesnt make it waterie and it is a stronger flavour. hope this helps xx