It is recommended you tack backwards in a mirror. It's easier to tack properly when you switch hands in front of you. The only reason you tack forwards in centre main boats is because the position of the centre mainsheet means you get tangled if you don't. Fast boats tack in a matter of about 2 seconds, and you should regularly look away from ahead of you to check your sails, look at clouds, the committee boat and other competitors for more than this, your field of vision isn't really an issue.