I've got a character that names all of his spirits -- not horribly weird yet....
I actually do that too.
My Spirit of Man (Men) named after the Musketeers, and show up looking just like one.
Beast Sprits = Puppy, Fido, Ubu. ........ and look like big black Hellhounds.
Water spirit named "River", couldn't decide if it looked like the a Mermaid or just a water filled human form.
Earth Elementals named Ben & Grimm, you can guess what they look like, hehe.
I wanted to give them personality & have some history there.
I've actually been wondering about spirit size. It says they are all metahuman sized but even that isn't completely clear since there is a world of difference between a Dwarf & a Troll.
I was thinking about a ratio of force to height/weight.
Base Height of 90cm (3ft) then add Force * 15cm (6in) and 20kg (45lb)
So, rough chart looks like this.
F1 3.5ft, 45lb
F2 4ft, 90lb
F3 4.5ft 135lb
F4 5ft 180lb
F5 5.5ft 235lb
F6 6ft 270lb
F7 6.5ft 315lb
F8 7ft, 360lb
F9 7.5ft 405lb
Not that they actually weigh that, just looking at rough size variations by force.