As I previously stated, engineered wood isn't suppose to expand and contract. IF it does, you won't see it. It's by design that it's not able to happen.
The butt-end to butt-end is NOT where expansion and contraction occur. In solid hardwood, if the floor is going to expand, it does so ACROSS the grain; NOT along the grain. In other words, the butt-ends are not the direction of expansion. PLUS, your floor is GLUED. Is your installer suggesting that when he leaves and (if) the floor is to expand, it's not going to eventually 'come loose' from the glue due to expansion??! Come on now!
I'll tell you what. Re-write your original question to the The National Wood Floors Association and see what they say. Do be sure to tell them the gaps are at the butt-ends and NOT along the sides. Then, you'll have something to 'give' your installer. Also, I suggest you write (e-mail) the manufacturer of your flooring in the same way. It I was you but I'm not but IF I were, I'd be darn mad! DO let me know what ends up happening.