It depends on the developer, cliveh. Many high acutance developers are formulated on the basis of controlled exhaustion - ie relative to fine grain developers they contain less developing agent and less preservative. This has a lot to do with how pronounced the edge effects get - particularly when you reduce agitation. Controlled exhaustion also helps explain why diluted fine grain developers do this too. But yes you are correct in saying the development time and agitation intervals (or lack of agitation altogether) play a very important role. If you stand-develop in D76 edge effects are more pronounced than if you agitate normally. However if you stand-develop in a high acutance developer it is possible get such pronounced edge effects that you clearly see contour outlines - even at relatively small enlargement sizes.