[Linked Image from coutelier.org.uk]

A thief was pretty much essential in your party in the old games due to the number of traps and locks. Realizing this the devs added Imoen to the start of BG1 to ensure there was always one available. She was written as the MC's childhood friend/sister who grew up with you in Candlekeep, then revealed in BG2 to be your actual half-sister.

On a technical note, there's obviously not much canon information about the heights of most of these characters. Last time I checked Forgotten Realms Wiki it said Avariel have an average height of just five feet. Although I've had other people insist they're much taller, or between 5 and 7 feet tall (which just seems like the normal range for adult humans, but okay). In any case, it feels right to me that Aerie is smallish so for the purposes of these I've made her 160cm (5ft3inches) tall. And Imoen similar; in fact just slightly taller.

I'd have done more, but for some reason this image has made me very sad.