As noted in other comments, shipping container stacks are a brutal RF environment. Have spent quite a bit of time with Iridium SBD in various applications and i

As noted in other comments, shipping container stacks are a brutal RF environment. Have spent quite a bit of time with Iridium SBD in various applications and it is rather sensitive to the surrounding environment. The wider and less obstructed the view of the sky from the antenna, the better. From a simplistic view - the satellite is flying over and dragging a beam a few kilometers wide over your antenna. The more time it has hitting the antenna, the higher chance you'll be able to get your messages up/down before it have moved on. If your antenna is buried under a stack of metal and has a pencil thin view of space - you're not going to be getting a lot of data across.