They were (AFAIK) high enough to only be reachable by non-man-portable long-range SAMs. i.e. truck-mounted or fixed SAM sites. The most recent transport shot down was above 20,000 ft when hit.

Flying through airspace where SAMs capable of reaching to your cruising altitude are in active use doesn’t strike me as a terribly bright idea. But hey, if you want to try it, it’s your life 🙂