Currently running a 3900. Two years ago, when we had our pool resurfaced, we had some steps put in, spa filled in, etc., and now a good third of the floor meets the wall at a sharp right angle (I didn't think about the curved floor at the time to accommodate the cleaner, nor did the PB). I had hoped to jimmy together some sort of additional wheel out in front that would help it climb, never got around to it, and getting sick of watching it hit the wall, stop, spin its wheels in place, run the backup cycle, and hope it turns enough during that to not do the same thing over and over. Even if the angle of approach is far from "straight in" (line of travel far from perpendicular to the wall), it still won't make the turn.
So now I'm thinking about alternatives to get around the problem. Will a Polaris 9550 climb a right-angled wall? Better question is, has anyone actually witnessed it first-hand?