You can do it with a sleeve grip, too. Difference with this and gake is that your arm goes under theirs as if doing Ippon Seoi Nage and as you drive and hook the leg, you fall into them positioned perpendicular to them, with the arm wrapping and body positioning creating a wrapping motion, hence it being a makikomi.
Thank you. Mostly, yes...I would also add the finish of the throw is different, typically you follow down to the ground with the Kouchi Makikomi as seen in the video, but with Kouchi Gake you tend to finish the throw in a standing position. I would say the action of the "hooking" leg is the same.