Just reiterating what has already been said really. Some of the best guys I've worked with have been your height or less, one guy served 12 years in the Kings and was assertive / good with verbals. Another was a European Kickboxing champion, had a good rapport with a lot of the rougher element of Liverpool and just knew how to deal with people, he wasn't afraid of getting physical either and used his training well.
It's all down to you as an individual. I will say that if you aren't confident in challenging situations then this will be picked up on by people, if someone is getting in your face or you ask them to leave and they come back with the old "Make me" or "Or what?" - And you hesitate then again, they will pick up on it.
If you havn't already I'd definitely go and train in a grappling based system - Judo, Freestyle Wrestling, Sambo would be my main suggestions, will give you a lot of confidence and the skills to back it up, they lend themselves very well to the shorter guy too. If you havn't got the size, you will need skill instead.
All the best, J