They are also very retardedly making themselves one nice target if ISIS has still any MANPADS left. Just because of that when Russians first came they flew riddiculously low and continously dispersed flares and only used rockets and guns for pinpoint attacking as fast as possible. When they ran out of munition they simply retreated fast like they cam, very low and zig-zagging. There should be a video of it on youtube.
Syria/Iraq is one flat country. There are no long hills or any terrain futures to get behind for choppers. When you watch the videos, many choppers shot down were simply cruising at high altitude in the middle of the daylight.