Theory: The 80 hit so hard and fast it blew its petals right away. Then you had a small diameter solid that made it through. A bullet of the same diameter and construction but higher SD will be heavier, and hence moving slower. Upon impact it will retain its petals farther into, if not all the way through, the penetration and hence make a better wound channel.
IMO, that velocity was better suited for that bullet. The 85 TSX may not open quite as quickly as the 80 gr. TTSX with it larger hollow point under the tip. I'd say you have a good combo there.
