ive noticed that hit percentage sometimes dosent matter in your rank, ive gotten an S ranking with a 10% hit rate on one level.... the thing i have noticed to get a S ranking on later levels is having a high level of heath. i have all the valks except for roys vf-1s, which you have to have all S rankings for every stage... the stage im stuck on is the last stage in DYRL levels.....trying to beat bodolza with 90-100% health left is really hard....also do a lot of rolls and shoot missles down with head lazers help the score too i think(but dont quote me on that last part!! )