My guess is that this change in arm angles won't affect your velocity much, if at all. Generally, when I've heard of a pitcher changing arm slots it has been in an effort to either increase movement and deception, or to change to an arm slot that is less stressful on that particular pitcher's arm. There may well be inefficiencies in your delivery that can be corrected, but I doubt that arm slot specifically is part of the problem or solution.
I would say going with the oft advised options of long toss, core work, and improved mechanics would be your best to improve velocity. Beyond that, experiment with arm angles and see what works for you. Ultimately, you have to find the arm slot that works for you rather than the arm slot that works for someone else.