For electric quadrupole ($E2$) observables, which depend on the large-distance tails of the nuclear wave function, ab initio no-core configuration interaction (NCCI) calculations converge slowly, making meaningful predictions challenging to obtain. Nonetheless, the calculated values for different $E2$ matrix elements, particularly those involving levels with closely-related structure (e.g., within the same rotational band) are found to be robustly proportinal. This observation suggests that a known value for one observable may be used to determine the overall scale of $E2$ strengths, and thereby provide predictions for others. In particular, we demonstrate that meaningful predictions for $E2$ transitions may obtained by calibration to the ground-state quadrupole moment. We test this approach for well-measured low-lying $E2$ transitions in 7Li and 9Be, then provide predictions for transitions in 8,9Li. In particular, we address the $2^+\rightarrow1^+$ transition in 8Li, for which the reported measured strength exceeds ab initio Green’s function Monte Carlo (GFMC) predictions by over an order of magnitude.