I personally know two pro’s that throw themselves up the neck on landing in the hunters. The frustrating part? One’s a Maclay winner!!!@#$ And they don’t do it on their jumpers. I can think of two fairly well known amateurs around here that do it as well, again they only do it on the hunters. Drives me bonkers. I’m so glad that all of my coaches over the years stick to correct equitation.
As far as two point in the undersaddle goes, I was always taught to sit in the eq and two point or half seat in the hunter u/s. One of my horses will happily canter around nice and soft if you are in two point, if your bum touches the saddle you better have the leg and hand ready to get him forward and round otherwise he shortens and becomes more uphill - a product of doing some jumpers and eventing as a young horse. My A/O hunter can get downhill, with him I sit softly on the short side to rebalance a little and then soften and go up in two point or a half seat so he can open up a little down the long side in front of the judge - this horse consistently places top 3 in the hack.
I’m not one to post at the canter. I don’t ride with anyone who does it either. At a show I may see one person do it, so it doesn’t seem to be a trend around here.