[Tobiah]

Practically any Delay plugin should behave as you expect by default,
I would have thought.

I would have thought so too. I was using reaDelay within Reaper.
I sends the first echo at 100%, and then applies the feedback
percentage after that. I always thought it was an unfortunate
quirk in that plugin, but I recently tried a couple of unrelated
free delay plugins and they behaved the same way. The problem
is most notable at lower feedback levels.