A different varient of a nebula which puts a strain on flux would be cool. A hazard which only the brave would journey through.
I intended to make a similar but not identical suggestion. While nebulas should included that feature which impairs flux dissipation (among other perils), we could have additional types of space terrain which also cause that effect. Make of them what you will: heat zone, radiation field, meteor storm, stellar flares, etc.; no reason why each shouldn't also have other degrading (and variable?) effects on combat performance as well.
Some variety of terrain that degrades weapons tracking (a natural source of ECM), or the flight endurance / self-guidance of seeking weapons, would also add originality and tension to a battle. Combine one or more of those effects with the one which impairs flux venting, and
both sides could be in serious trouble even before the first shot is fired. Once you add some ship or fixed installation that must be rescued or attacked within such an area, you've got yourself one exciting and unpredictable situation; where staying "out of the soup" is not an option.