Kind of a silly question but worth checking....are you trying to carry more than just the head while you are false casting?
It's been a few years since I've thrown an OBS, but I used to fish those lines a ton, and if I recall they aren't very forgiving when you get much more than the head out of your rod tip. With that short of a head, if you're doing much false casting and super focused on distance perhaps you're losing distance when you let more than just the head out and the weight of the head is collapsing the running line? Perhaps with the new, faster rod you're trying a bit harder to keep up and letting out a fair amount of running line while false casting and not even realizing it?
Just a thought that popped into my head. Shooting head lines aren't designed to really carry much more than the head itself while casting, but I find some to be more forgiving than others in that department. Fishing the Cortland Compact a bunch the last couple of years I find that I can carry the entire head plus a good 10' or more of running line without any issue, but I seem to recall the OBS being a line that didn't respond well to that.
Just a possibility. I'd say there is likely something going on, either with your cast or with your setup. The OBS isn't a distance line in the sense of super long, competition style casting, but I always found that to be a line that would throw 45-50' almost on its own. A false cast or two to get the head out, hauls to build line speed, then a nice high stop to let er rip. 50' is a distance that can catch you plenty of fish, no doubt, but its also a distance that in general I've always felt was really easy to achieve with that line when I focus on keeping things simple and letting the line do what it's designed to do.