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Much smaller to the point where it would no longer be a snug fit?

It really depends on how tight the sleeve actually is. From left to right is where the real difference in size is (keyboard direction length). I guess the only way to know for sure is giving it a go :). The good news is amazon is easy to return items to.
 
Much smaller to the point where it would no longer be a snug fit?

It isn't smaller than the air in all dimensions. The front to back dimension is longer than the 11" MBA due to the 16:10 screen vs. 16:9 in the 11" MBA. Take a look on Apple's specs page, it has the dimensions listed.
 
I don't recommend that sleeve for any notebook. Little protection and very rough exterior. Feels like burlap. I bought one last year. I tossed it out.
 
I'm still enjoying my Level 8 11in case with the new rMB. It's cheap, neoprene with plenty of protection for my needs, and has a zipper pocket for adapters. I will probably grab a nice new high end case eventually, but this is an excellent choice in my opinion. The rMB is not as wide as the 11in so there's a small gap, but overall it's hard to tell this case was not made for it. If you know you are going to be carrying adapters around, the pocket is great as well.

https://www.level8cases.com/products/11airsleeves.php
 
I use the incase 11" macbook air sleeve for my MBP and it works great. Little tight but not a bad solution at all, probably the best on the market at the moment.
 
Yes, the macbook is smaller than the 11" Air.

jeez people... you should get your facts straight. The rMB is smaller in the long direction (i.e. direction of the keyboard) but slightly larger in the other direction (since the screen ratio between the two are different) making the MB more square and the MBA more rectangular.

Dimensions are on the Apple site under tech specs for each.

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It isn't smaller than the air in all dimensions. The front to back dimension is longer than the 11" MBA due to the 16:10 screen vs. 16:9 in the 11" MBA. Take a look on Apple's specs page, it has the dimensions listed.

This... which i guess is what I said before I noticed it was said before me.
 
jeez people... you should get your facts straight. The rMB is smaller in the long direction (i.e. direction of the keyboard) but slightly larger in the other direction (since the screen ratio between the two are different) making the MB more square and the MBA more rectangular.

Dimensions are on the Apple site under tech specs for each.

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This... which i guess is what I said before I noticed it was said before me.

correct. Most 11" cases work for this reason
 
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