Just in case it helps anyone that comes along and reads this thread later…..
I got a few more lengths of conduit and they measure between around 25.05mm and 24.7 mm as you rotate them and they’re a much better fit.
No more slop in the roller assemblies even when they’re not tensioned and they’re a tighter but still smooth fit everywhere else. Would still like slightly more tension on the roller F sections but maybe that’s just me.
For anyone trying to use inch (25.4mm) conduit, if the variance in diameter is as much as I’m finding in the metric conduit then you should hopefully be able to find a few lengths that are undersized and use those.