Vertical plume induced instability - Hydro versus NBQ

I have performed few runs with PSOURCE_MASS (vertical point release) from the seabed, with HYDRO and NBQ and it appears that both work, but with differences in the results.

When I release high salinity water (heavier than the overlying seawater) both HYDRO and NBQ simulations give almost identical results.

When I release a buoyant plume with initial density lower that the overlying seawater (50PSU but hot 55 degrees C) there are significant differences. At that initial temperature the released brine has less density than the seawater above and it creates a water column instability.

My question is, does the NBQ simulation handles the instability better? Theoretically I would expect so since it makes less assumptions about the water column stratification? Is it better to handle such cases with the NBQ solver?

I am attaching couple of figures that show that in HYDRO mode, the brine plume appears more buoyant than in the NBQ runs. In both runs the plume is released at the deepest point of the bathymetry depression (dark blue in bathymetry graph), but in hydro mode the plume has completely escaped the depression whereas in NBQ mode, only a small portion has escaped after 24 hours.

Many thanks for any feedback!
C:\fakepath\Buoyant plume - hydrostatic.png
C:\fakepath\Buoyant plume - NBQ solver.png