Everything you said sounds good: string blur, back tension, increased accuracy. The only thing I wonder about is your anchor. Are you anchoring in the corner of your mouth because that is your natural anchor or because you read somewhere that that was a good place to anchor?
What I would like is for you to forget about your anchor for a moment. Instead concentrate totally on form. Draw until your forearm is behind the arrow, and your shoulder blade is pressed against your backbone. If it helps, keep the arrow away from your face while you do this. When you bring the arrow to your face, the arrow should be under your dominant eye, and you should be aware of string blur. If your finger lands in the corner of your mouth, fine. If not, find new anchor(s) to fit your form, not vice-versa.
Who knows, you may get back part of your lost draw length. If not, then 27” must be your true draw length.