Hi all need some help and advice plastering reveals, have noticed slight arching in the corners (not square nice right angles) where the head of the reveal meets the wall, tried corner trowel while plaster wet and as firming up,tried picking out corner with the toe of the trowel, tried just troweling out from window towards, troweling down bead, not to much plaster on trowel to start etc... Really driving us mad!! Any advice will be great! Cheers