When you say, " I have a single backstay, and don't want to create a 2nd attachment point on the stern as many systems I've seen do", I assume you mean that you don't want to go to a split backstay system, like this (or similar):
Having a split backstay with a tensioner gives one a more fail-safe system. If any one component below the plate that actually splits the backstay fails there is a pretty good chance that the mast won't fall down. If you just had a set of blocks (or a cascading system) the failure of a block or a bit of rope could cause your mast to have little or no aft support.
Never forget them. Do something to prevent it from happening again.
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