I did some testing with my orbital last week to see how much agitation was needed to cover the film adequately. If I use the base and rotate by hand there is a lot of movement round the edges with just a little across the inner sides using 300ml of fluid (tested with used film and the lights on). I experimented for a while and found that the gentle agitation discussed here worked very well with just a small amount of movement needed to cover all four sheets of 4x5 using 150ml of chemicals. The best method of all seemed to be 15 secs of Manual rotation followed by gentle side to side tilting.
In the past I'd simply used constant rotation which usually delivers well enough developed negs.