This will track rotation / position and scale with camera. See how I get large when camera comes in...

All text-markers should have a rotation of 0,0,0 and scale of 1,1,1 when facing the camera when the camera is at 90,0,0 (use apply transform). From there any transforms should be applied.

I'm a billboarded text that always faces you and stuck to the top right corner of this box. I also don't scale :)