Hat 2 (and a size difference)

 I finished the 2nd Lime Green Hat last night.  It's the one I made using the Bates Inline hook that I favor.

I put both the green hats together to see if there was a difference in size, and there was.  The 2nd hat is in the back.  I used the exact same pattern for both hats, but different brands of hooks.  I used a size H for both brands, just to be specific.  Obviously, the Boye hook I used for the 1st hat is giving me a smaller product.  I wonder if I actually crochet a tighter piece because of the type of hook?  It's a possibility.