143.5 is not ‘the’ boost length. New RF axles are 136mm for boost but they used to be 134mm. 136mm gives 52mm chainline. The qfactor and chainline documents specifically references flipping the chain ring to adjust chainline.
143.5mm is an alternative for bikes with wide back ends. I’ve got one of those on my Tarn ti to give better heal clearance on the chain stays. It’s gives quite a wide chainline (55.5mm I think).
Aftermarket rings have a variety of offsets with cinch mounts. On my Tarn I’m using a non-boost one up ring to move the chainline back in again.
There are also about 3 more longer sizes to accommodate superboost and fat bike.