The Refremas are in a complete league of their own. Terry Khan spent his whole career going from lab to lab in NA and beyond adjusting the burst systems to get even flow.
ND tests would be done on E6 film , basically neutral lit gray backgrounds and then processed on a full rack which would hold 6-10 4x5 at a time.
Terry's drill would be to evenly match the density on four corners , middle , top and bottom.
Colourgenics in Toronto would bring him in for tune ups on their machine and were cherished by commercial shooters who needed even and consistent development.
The burst was adjusted top to bottom side to side to even out the agitation in the larger tank.
Burst from the bottom in smaller tanks only will agitate the film but certainly not even as suggested by some here.
Originally Posted by CGW