WAIT STOP. All of the Second Doctor's companions are short kings/queens. At least according to this site. I mean Nicholas Courtney as the Brigadier was taller than him but he wasn't really a companion.
I had read somewhere Patrick Troughton and Frazer Hines were shorter but I noticed it especially because Wendy Padbury is quite shorter than them (Deborah Watling was too.)
In looking at that site almost all of the companions have been shorter or the same height as the Doctor (up until I'm guess Jodie Whittaker's Doctor, who isn't on this site.) Notably Peter Purves (Steven) and William Russell (Ian) were taller than the first Doctor, but after that nope.
While I'm sure that doesn't go into all of casting I'm sure it helps a little bit for the companions to be "below" the Doctor in order to help the Doctor demonstrate the leadership and brilliance standing out as most tall.
