If its the same as the Tomcat, you still have to tell where jester to look sometimes with the jester wheel, to specifically focus the search on to a certain piece of sky.
Also, if you were chasing and there was relatively little speed difference, you won't be able to get a lock, no matter what radar you have in DCS, due to how these radars work, as they will be in the notch. In that situation you either need to slow down or speed up to create a positive/negative closure rate, and get the targets out of the notch.
Most radars have different settings used depending whether the target is hot or cold as well, and being in the wrong prf greatly reduces detection chance, if your radar is set for hot targets and they're cold for example (hot target is coming towards you, cold target is flying away from you). Jester can need a prod in the right direction with this sometimes.
Re sidewinder, no idea....