Well, you have to keep in mind that I live in Croatia:-)
All non-Croat Alexandras I've met were
Alex and in Croatia the nicknames for Aleksandra/Aleksandar are Sandi (m), Aleks (m), Aco (m) (pr. Ah-tzo),
Sasha (m&f), Aleksa (f). I guess that in UK/US
Lexie might be more dominant.