Do you have record engaged?
I think I ran into this as well, but am only like 3hrs in w/ mine. My understanding: When you don’t have record engaged you’re hearing what would be fed back into the tape on the next record. So at -5 where it would be overwritten there’s no sound. At -4 I think what you’re hearing is an attenuated and compressed version of the sound that would cause it to regenerate like a delay w/ lower feedback if you turned record on. at cv nearing 0 the tape compression tapers off and you are hearing the full volume of the sound so that it would regenerate 100% if you had record on.
W/o record engaged it’s not that different from volume control (except with a little compression) of the loop, but with record engaged around -4 will turn the current pass through the loop into a quieter/compressed “faint ghost” on the next pass.