If you use a peep or some peep elimination device, you've got two anchor references. The contact spot on your face/jaw is the primary. The peep or other device is the secondary.

I tried that 'string to the nose' reference once, long ago when bows were man-sized ,but I got tired of always having a scab on the tip of my honker.[8D]Never could keep the string from ripping off a layer of hide every time I went shooting.[&:]