Uprights should be closed off and anything over it is no good.
I am not sure if you are joking or not, but I have actually thought that this would be a good idea for a long time. It would make short, chip shot field goals more difficult, as kickers would have to alter the ball's trajectory to fit it in under the crossbar that would run from upright to upright. This would lead to more field goal blocks, which are always exciting. This would obviously encourage more 4th down attempts in the red zone. It would also encourage more 2pt. conversions. And it wouldn't affect long field goal attempts, as the bar would rarely come into play, being at the top of the upright. I think that somebody should propose this to the powers that be in the NFL.