?

The only way that a 1/2 wave mode can be supported is to have a node at the top and closed bottom of the pipe, and this fundamental would be twice that of the 1/4 wave mode. In this case, that would be 80 Hz. Since the 1/2 wave mode is trapped between the ends, it would produce no output but would modulate the driver. I don't see it in the model above, nor do I remember you mentioning 1/2 wave modes in stopped pipes.

See Modeled/actual comparisons.

Bob