(2 months too late to reply!) The portals can't open at angles on vertical bricks. They can on terrains.
They do function at an angle, it's just that there's a slight problem with the emitter code that means I can't (haven't figure out how to) make the emitter appear right on angled bricks. If you place a Portal on a 45 degree ramp, it'll work fine, but appear to be at an odd angle.
