The Synik 22 product page says "The Synik 22 fits laptops up to the size of the 13” MacBook Pro (but not the older non-Retina Air) or the Dell XPS 13". I have a 2012 13" MacBook Air (sadly not working now, and I'm still thinking about whether to spend the money for a part that may or may not fix the problem) and a 2015 13" MacBook Pro (on which I'm typing this), so I can give photographic examples of how they fit.
First I tried putting the MacBook Air into the sleeve from the top opening. It did actually go in, but I had to wiggle it in (it was almost too wide to go past the zipper) and once it was in, I could see that it was stretching the sleeve material where the backpack's frame curved away. So you could actually carry it that way, but I don't recommend it because it's likely to put too much stress on the sleeve and its zipper over time. There's nothing to stop you from putting it in the main section of the backpack, though, or even in that pocket on the front wall of the main compartment.
Photos, clockwise from upper right:
13" MacBook Air in sleeve of Synik 22
An attempt at showing how the sleeve material is stretched by the Air, but it's black material in shadow so you can't actually see much there
13" MacBook Air lying in main compartment of Synik 22, for size comparison
13" MacBook Air in the flat pocket at the front wall of the main compartment
Then I did the same with the MacBook Pro. It slid right into the sleeve, and the top of the laptop was maybe half an inch or so (around 1 cm) below the zipper. It too stretched the sleeve material a little, but not as much. I was also able to slide it in and out through the side zipper, with a small amount of wiggling to turn it a little.
Photos are same as above, but with a 13" MacBook Pro instead of the Air.
One further note on the laptops stretching in the sleeve material: with both laptops, the sleeve stretch was most noticeable where the Synik frame curves. I tried taking out the frame to see how that would change things; it did reduce the amount that the sleeve needed to stretch there at the side, but somehow it made it even more noticeable that the top opening is really just a little too tight for the MBAir. (I didn't even try it through the side opening, it seemed so unlikely to fit through there.)
P.S. Since they've often been commented on elsewhere: my beautiful laptop skins are both from DecalGirl. The forest scene is the work of Digital Blasphemy, the calm waves are by Shell Rummel.