Why not mine the entrance to the system where you met the new ... more dangerous aliens?
They are hostile wiith you already, and you don't risk to start an avoidable shooting war with the Charlies...
Well, assuming the mines only target hostiles, it would make sense to work outwards from SOL, and quickly, rather than having to constantly cross a larger distance, and risk losing the ship at the start of the operations. Once SOL is secured, then expand and place these mines outwards at the jump points at Procyon etc