Tips on reducing friction from my forearm against the desk

Im relatively new to PC gaming ~ 1200 hours over a little over a year. And very new ~300 hours to shooters. So, naturally I've been aim, training and doing what I've seen recommended across the Internet space such as limiting your aim training to about 10-20% of your total play time in a day. So if I'm playing for 3 hours I will aim train for about 18-30 minutes, then take a break then get in game.

But through this I've kept having this continuing issue, I've gotten a compression sleeve like people have suggested to reduce friction, but I still feel my up and down motions have more resistance compared to my left and right movements. What would be the best way to go about rectifying this and making my longer diagonal flicks more consistent, which are by far my weak point? Desk is solid wood and polished and I have a ultra thin mousepad that isn't noticeable when I move my arm up and down my desk.