We are now getting
multiple reports that officials within the Pentagon are confirming that this was an MQ-4C. This means the aircraft secretly deployed to the region. They are also adamant that the loss occurred in international airspace.
It's important to discuss the MQ-4C's capabilities here in context to the situation. It is not just a standoff radar, imagery, and electronic intelligence gathering platform optimized for the maritime environment. It uses its MTS electro-optical turret to check targets out in detail by dropping down to lower altitudes and approaching them. In other words, it is meant to fly at lower altitudes as well as higher ones, unlike the Global Hawk. It also has a lower operating altitude than the RQ-4 in general. It has anti-icing systems for penetrating bad weather because of these factors. So there is a chance it may have been operating at medium altitude, or even lower momentarily, depending on its mission profile and what its operators were seeing. This puts it into a larger number of SAM systems engagement envelopes.
MQ-4C isn't just a 'blue water' surveillance tool. It can watch areas of interest in the littorals and keep track of an enemy's actions in a high fidelity manner. It is an amazing system. The closer you get to say a port of interest the better the quality of certain types of intel it can gather. So just staying far away means you are not maximizing the aircraft's unique capabilities as a multi-intelligence gathering platform. Fusing radar, electronic, and image intel together—all of which the aircraft can provide—over long periods of time is really why its capabilities are so awesome. To get the best out of all three, closer proximity to a target area may be required. So there are tradeoffs when it comes to risk versus reward.
Also, if this was indeed an MQ-4C on its first deployment, a secret one, remember it would have been totally new to the Iranians too. They could have been seeing a Global Hawk doing stuff a Global Hawk doesn't do. This would draw interest and likely targeting priority.