Before suggesting actresses like Elisabeth Sladen or Julianne Moore or Glenn Close, let's remember that at least during TNG-ENT all actors cast as male Klingons were to be 6'3" or taller, and all actresses cast as female Klingons were to be 5'7" or taller. The tallest of the three I named is Glenn Close, at 5'5". This may not seem like such a big thing, but Klingons have a reputation as being physically imposing, and some tiny little actress with attitude will usually only come across as bitchy, regardless of her talent or the skill of the makeup artist.
Not all of them. Robert O'Reilly is 178 cm/5'10.25".
http://www.celebheights.com/s/Robert-OReilly-474.html That's not particularly tall, and Gowron certainly made a badass mofo Klingon chancellor.
Christine Rose also played a Klingon in "Birthright 2", and she is 5'5" (165 cm).
http://www.imdb.com/name/nm0004284/bio
Besides, it all depends on the height of their co-stars. Worf had to be played by a tall actor to come off as physically imposing, because Riker was very tall. On DS9, most actors and actresses were tall, so it was easier for the Ferengi actors to look very short. Shimerman didn't look that short on
Buffy when he was playing against Sarah Michelle Gellar (who makes almost all of her co-stars look tall and big). Put an actor of an average height against a very tall person if you want them to play a Ferengi, and put them against a small person if you want them to play a Klingon, and problem solved.