So if you succeed while double shooting, you only actually put down one mine, right? Seems kinda... weird. That you fire off two mines to make it more likely to land a single mine while one is always guaranteed to disappear into the void.
You're missing context of what makes you post this, I think. Double Shot gives you a burst of 2 (edit: Burst 1 with a +1 bonus makes 2 total). In active turn that means you can distribute shots on two different target locations. In reactive turn you are limited to only targeting one single location. You should be getting burst 2 here (not confirmed yet), but will only be able to place one mine physically.