The way I've been looking at this is that FF has in mind:

A) a situation where there is a limit that must be gotten above before whatever is accomplished. This is the normal "exceeding the threshold."

2) contrariwise, there is a situation where there is a limit that must be gotten below before whatever is accomplished. Given the root definition of threshold in English, I would say that that is not the word to use in this situation. All due respect to Nuncle, but I don't think that the Latin limen is a good translation for the English threshold.

Þ) I would suggest dropping the threshold word entirely and starting over, just with the term lower limit.