The new HI gradient stuff finished down to z=3.  Turns out it does make a small difference in the calculated Sobolev values of this particular galaxy.  At the same time however, we find now calculate the HI surface density via the grid calculation and drop that along with it, so the difference between grid & sobolev remains about ~1dex:(plot made via gal_reduction/tools/sigmacompare.py)

Sigma_HSML however remains a front-runner here as it’s separation is only about ~0.5dex or less depending on if we account for the spread.  2xSigma_HSML overshoots the grid calculation by a tiny bit.  In comparing these two galaxies I’ve also found that the Sigma_HI results in slightly less stellar and gas content:

It’s not entirely clear where to go from this point or which option is the best option to estimate the surface density within these SPH sims…