actually Tech was pretty big when they first showed him
but then they made him small again during Impel down
only for him to be big again
Oda is somewhat inconsistent with height
I remember during Marine Ford the shichibukai were towering over the marines
of course Flamingo and Kuma are tall as well as Moria but Hancock was towering too lol
I think Oda just brought him back to his original height