To confirm the predictions described above, we conducted 1,296 controlled matched-pair experiments using RAPID (see Supplementary Material for full experimental details). Each batch of 96 experiments consisted of 48 matched pairs, whose compositions were sampled over the possible organoammonium iodide, lead iodide, and formic acid concentration space. Sampling strategies included: (a) uniform sampling over all achievable compositions, (b) uniform sampling over compositions where the formic acid concentration was between 7-10 M, (c) uniform sampling within the convex hull defined by previously observed crystal formation.