One should also try to minimize the reference pressure bias. The smoothing of the density profile needed to prevent folding will be overshadowed by the density discretization process if the density steps are chosen sufficiently large. However, the clean separation of isoneutral and dianeutral mixing will be lost to some extent. A partial cure for this would be mixing tensor rotation. Extending them over large horizontal distances leads to ambiguities, such as helicity.
Isopycnic models are free of the pressure gradient error found in sigma coordinate models.