Thanks for the side by side view ErikH. It seems that the stem is long enough and the position of the triangle is fine. We just need to modify the arrow head ever so slightly larger (to be able to move the tip slightly higher than both '55' and '5'. Whether or not it is obvious in real life is another thing. Laco might have started a template already?
Thanks Bruce, looks like 9mm would be a little too big? I measured my Archimede 42mm and it has an 8.5mm diamond crown. I think with an onion crown, 7.5mm to 8mm would be suffice proportionally.