Palm rejection

I'm trying to implement palm rejection (ignore palm touching screen) in a game that will be played using a stylus. I'm using touch.radius to check that the radius is less than the max radius and only using those touches. This seems to work however during testing on a Samsung A7 tablet I noticed there are 0 touches if I lay most of my hand on the screen.

Is this standard across different tablets? Is this something that can be toggled on or off or is it a limitation of the hardware?

Thanks for any input.