Aviod major battles. If you have your cloaked escort fleets thinnly spread out, then you can't afford losses and damage. This works properly with torpedo ships. As the enemy charges along, you will blast them until they get in range. This chart has been made so you can judge how invisible your fleet is.
All numbers are mathmatically correct.
Anything below that, then I can almost guarantee you will be seen. There is a bug that makes it so when you spy, instead of resources being devoted to the fields you spied on, it is spent on the current field your researching. Will be fixed with 2.6a. Their orders have been canceled. There is yet another bug since 2.5 that affects SS only.