It's the way it is. Final Fantasy 1, 1st boss. Garland is a normal sized knight, but in battle he's doubled the size of the player. Hence, Gale is the same thing. It's how the old FF's worked, bosses were always huge.
I thought it was appropriate that the first boss battle would be like Final Fantasy 1's first boss battle., the first WIDELY popular JRPG. I was supposed to mention the size thing in the comic, but I thought that people would recognize the older FF's.
Luckily there will be only five more.