HT Subwoofer port tuning mistake... Looking for redesign insight

Sorry for the late reply.

This is of course a side topic, an important one at that. I think the original question has been solved though with the pointers in posts #2 and #5. So it should be all good.

There is some published research on this effect. Trawling through the internet it's hard to find a succinct reference, but below is a graph showing the effect on tuning frequency of locating a square orifice at different locations on the face of a cubical cavity

The graph below is from a thesis referencing "Effects of geometry on the resonance frequency of Helmholtz resonators" by R C Chanaud. I can't find a free copy of the original paper.

What's shown, as described right at the bottom of the graph, is not "the effect", as you term it, but the predicted effect. It's a calculation / simulation, and as such a thesis.

Established & commonly used to separate fact from theories, beliefs and fiction, is something called "the scientific method". Simply, a thesis needs to be put to a practical / empiricial test to be proven or disproven.

In this case, the experiment would entail a comparison of simulated / calculated (via the correction factors that you speculate lead to accurate results) vs. measured results of the tuning frequency of bassreflex speakers with various types and locations of Helmholtz resonators.
If simulated results match well with measured results over a wide variety of enclosure / port types, without any notable large exceptions / deviations, it should be accepted as proof.