(Edited for math:)
Running the math through my head...I've run into a bit of an issue. If the particular building Free is on is about 800 feet high, and Diabolus is maybe 50 feet from the base of said building., taking into account Free would be standing on or near the edge to get a visual target, if he fired a 45 degree blast from that height centered on Diabolus, we are talking a nearly 300 foot blast radius. Given these parameters, the building Free is standing on would be well within the blast zone. I would be fine with altering the post to take the angle of the blast into account, centering instead on an area roughly 200 feet or so away from Diabolus. He would still be in the radius, but the Building wouldn't be. Otherwise, depending on how long the beam lasts, Free will probably fall into it when the building does.