Not really, no. Please forgive me, I think I just misphrased my findings.
I would be directly on top of the AP, and the signal would be at a level of X dBm. Then I’d move approximately 1.5 meters in any direction, and the signal level would change, to Y dBm. The value Z=Y-X was approximately +20 dBm. The signal was boosted when I moved away from a position directly above the AP, but that doesn’t necessarily indicate constructive interference, since it was getting blocked in the first place.
I didn’t measure a before and after, since I was only interested in the effectiveness of reflective surfaces proof-of-concept-wise, so I don’t know for sure whether the signal was getting boosted relative to the baseline. I had a vague idea of the baseline, though, and even if it was getting boosted where it shouldn’t have been, it didn’t feel like it was by much.