You really can't mate the half-rounds too tightly unless you have stretched the Monokote as you applied it. If the hinge line is truly straight, binding from Monokote hinges is difficult to achieve. On the other hand, a small gap is unimportant because the Monokote hinges, being full span, seal the hinge line completely anyhow. I would suggest that you aim for a smooth, snug installation, but without being a fanatic about it.