Fluid particles simulations

Simulation 1 : 2000 particles involved / different fluids' viscosity in a cube.

I played with different settings but still don't understand the following:

1- why particles agglomerate to the wall? (and do not respect the interaction radius value...)

2- why one fluid doesn't migrate over the other? (the two fluids have two different viscosity values)

Simulation 2 : two fluids particles (6k) with different mass

The fact that the fluid doesn't migrate over the other is due to the mass and not viscosity as demonstrated by the next video.

Simulation 3 : two fluids particles (12k) different mass and thick frontwall

Blender keyed particles system with path option - Tutorial

 The two particles systems to be keyed must be created first. In this example, one for the cube and one another for the sphere.