Am a "JKD" guy (whatever that is), FWIW. Have been taught both ways, by different camps (OJKD/"concepts"). At the end of the day, I doubt that in fighting, sport or not, it's probably not going to make as much a difference if your fist is vertical or angled when doing a jab. Also don't think that nerding out on one way or the other is going to help as much as working on another relevant skill: sweeps, use of tools, sprawls, defense of GnP etc. If you've already got a pretty broad and relevant foundation, cool.
I tend to have my fist vertical, incidentally. In part because of comfort, in part because it more readily allows me the use of other tools, in part because I feel like my jab gets through the other persons' defenses more often. Would advocate that your concern matters more with a cross, when body mechanics seem to more substantially dictate having your fist horizontal. Don't think that's as much a concern with a jab.