Function default_surplus_for 

pub const fn default_surplus_for(threshold: u8) -> u8

Shares to emit per polynomial beyond threshold, to absorb losses.

A ratio, evaluated at the threshold actually configured — see SURPLUS_LOSS_TOLERANCE_DIVISOR for why a ratio is the physically meaningful shape.

This used to be a bare constant, DEFAULT_POLY_THRESHOLD / 2, evaluated once at the default threshold and then applied whatever the configured one was. Deployments run thresholds from 16 to 64, so a single absolute surplus means wildly different insurance across that range: a flat 20 covers 24 % loss at threshold 64 but 56 % at threshold 16, where it exceeds the shares it insures. Since H5 the surplus is billed on purchase rather than on claim, so that over-insurance is quota an Entry pays for in every deposit.

Rounds up. The result is a guarantee of at least the documented tolerance, not an approximation of it: shares are indivisible, so a threshold that is not a multiple of SURPLUS_LOSS_TOLERANCE_DIVISOR has to land on one side of 20 % or the other, and covering less than the documented rate is the failure this function exists to prevent. Rounding down undershot for every such threshold — 33 received 8 surplus shares and covered 19.51 % — and gave thresholds 2 and 3 a surplus of zero, i.e. no loss tolerance at all, at and just above MIN_POLY_THRESHOLD. Rounding up over-covers by less than one share, which is most visible at the smallest thresholds (2 → 1 surplus → 33 %) and vanishes as the threshold grows (63 → 16 → 20.3 %).

The deployed value is unaffected: DEFAULT_POLY_THRESHOLD is 64, a multiple of the divisor, so this returns 16 either way and no negotiated quota moves.