One of the stated intentions is not to allow a strop instead of the bail that would effectively reduce the amount of mainsheet. The bail is the bridle system with the U-Bolt on the boom and where the mainsheet attaches to the boom. What you describe for attaching to the traveller is the intention of what the rules allow. I'm sure the class measurer will speak up if there is anything wrong with it.
I recall this same discussion on the forum several years back.
Edit: Found this old link on Mainsheet Strop