2) Even terminated to a point, it's never zero since the molecules 'stack up', creating an acoustic boundary plate of 'x' dimensions, just as BB found out through experimentation.

3) BB simmed a design that got good reviews and concluded that it sucked from a technical POV due to the pointed termination, concluding he would never use one. His loss IMO since it can be used to good advantage in some apps since it loads the pipe/driver much more than a larger closed end.

4) Yes, you get excessive ripple, it's the reason for making the pointed termination, but this can be tamed as desired by proper driver/stuffing placement.

Consider a woofer with a high Le. You sim a T/S max flat ML-TL and the LF gain follows the sliding slope below ~100Hz, so it's not so half space flat. With a pointed termination positive tapered pipe you get much more gain down low even after rolling some of it off through driver/stuffing placement, with the side benefit of a much better impulse response.

GM