logit
The combined weight on the logit at the supplied centered probability, formed by summing every coefficient whose basis term carries the logit, each scaled by the matching power of that centered probability. Terms two and three carry the logit, as does every even-numbered term from six onward.
Evaluated at plus or minus one half, this governs the behavior of the quantile function in the corresponding tail. A strictly positive weight means the quantile function diverges logarithmically there; a weight of exactly zero means it approaches a finite limit.