The Bobby AI leads their target even if it is using beam weapons, this causes them to miss relatively small targets at a close distance, and medium targets at a larger distance.
Something the size of an isanth at 1/1.5KM range will most likely not get hit if it is moving:
{F160}
Keep in mind that some AI turrets have mixed weapons, so the AI would need to lead their target for the cannon/missile part but not do that for beams.