As a winger in a 4-3-3, height shouldn't matter that much, plus its not as if Nani is tall at 5'9.
Nani is VERY enigmatic, and why spend the money on a guy like him when you have an inconsistent, talented footballer in Giovinco already. Both are right footed, and both are best as wingers.
IMO you buy versatile players.
These are just examples but guys like:
Modric - CDM/CM/CAM
Turan - LW/LW/CAM
Di Maria - RM/LM/RW/LW/CM/CAM
If we're going to play around with formations, getting Nani is stupid, especially when we have a player with almost identical attributes on the bench, who is younger & italian.