Reference-state dependence and interface scaling of superfluid response in a two-dimensional crystal

Grain boundaries modify both transport paths and the surrounding crystal, making their contribution to superfluid stiffness difficult to isolate. We quantify these contributions in stationary two-dimensional soft-core Gross--Pitaevskii (GP) crystals using tensor response, independently prepared bicrystals, and measured interface lengths. A one-percent change of lattice spacing alters the bulk stiffness by approximately 5--9\%, comparable to the boundary contribution. For the same defective state, two bulk references give relative excesses of 0.027\% and 4.15\%. Matching the comparator to grain strain and chemical potential yields positive diagonal excesses in paired preparations at three interaction strengths. Within a twelve-state family with comparable grain interiors, the excess is robust to 288 bulk substitutions and follows an approximate length-per-area relation. Independent fixed-area pairs yield a line-response coefficient 3.1\% higher than the three-size estimate. Size and directional dependence restrict this relation to the specified crystal conditions. Reduced link networks relate the directional response to the organization of boundary connections but do not accurately resolve every small bulk-subtracted excess. The results distinguish boundary enhancement from changes in the surrounding crystal and establish a quantitative comparison protocol for superfluid transport in defective crystals.