I don't think you would have excess paradox with a longer shaft. You would if you just took two identical shafts and cut one longer than the other. However, then one or the other of them would not be tuned for your bow.
If you take two shafts, both of which are tuned for your bow, one longer than the other, I believe the longer one will actually have less paradox than the shorter one. For both the shorter and the longer shafts to be tuned for your bow, the shorter shaft would necessarily have to have a weaker spine than the longer shaft, and therefore would have more paradox than the longer shaft. Or possibly the weaker spine of the shorter shaft would be offset by the extra length of the longer shaft, so they would both end up with the same dynamic spine in order to be tuned for your bow, so possibly the paradox would be the same, I'm not sure.
There may be other reasons for keeping the shafts as short as possible, but excess paradox on the longer shaft is not one of them.