Bottle vs. Sippy.

We got our one year old a sippy cup, it's one with a straw.

He has the whole sucking thing down. When hes sitting in his high chair and i give him water in a bottle he tries to suck it like a straw.

But if I put water into his sippy he just chews in it. The tips are made of the same material so I dont really understand it i guess ?

Any suggestions on how to get him to use it correctly ?