Jan -
Just to try to consolidate some of the information that's in this thread...
With TR, once you are no longer new at managing your cat's numbers and are
data ready you are able to think in terms of shooting progressively lower numbers. You've shot a reduced dose with a PMPS in the 80s. You might want to think in terms of what number you'd be comfortable shooting.
Ideally, you want to be able to shoot any number above 50 providing you're not seeing dropping numbers. There was functionally no difference between your +9 (at 80) and your AMPS of 67. (There's a 20% variance that's due to the meter so these are essentially the same number.) For most cats, Lantus onset isn't for 2 hours. In addition, you're feeding your cat at shot time. Between the influence of the previous dose wearing off, the window of time between feeding your cat and Lantus beginning to work, numbers are typically rising until approx. +2 so you have a reasonable margin in which to shoot. Further, shooting low often results in a flat cycle.
Obviously, with shooting low you want to have the ability to monitor to insure your cat is safe and/or have enough data to know how your cat responds. Likewise, I would never advise someone to shoot low if they did not have strips and high carb on hand.