I would say the curve shape matters more than the silence level. I think we may as well have this as another choice (not worth bringing back the mid-fade slider) .
There is also potential for confusion with a % scale.
I don’t think there is much potential for rank beginners who don’t know what a gain is, given percentage is common understanding (percentage of something).
Such confusion as there is will be with the “Gain” word when combined with %. I agree that users who think about it a bit more could guess that 20% gain is really 120% or 1.2. In fact, % hardly seems like a “gain” at all, per your comment above, but it’s very useful.
The problem with “Linear Scale” as a wording choice (apart from people understanding that 1 is unity) is that it directly invites thinking that e.g. 0.1 is a target that moves the amplitude to 0.1 on the linear scale to left of the waveform.
So, here is one possibility, distinguishing “% of original” from both “gains” (I’m not sure about adding “(1=original)” after “linear”, as it may confuse with “% of original”:

Would “(1=unity)” be better (I doubt it), or “(1= no change)”, or no explanation?
I want to add that I care more about % being there than worrying whether we distinguish % from gain or not - but I think distinguishing it gets over any objections that % is “confusing”. “Gain as:” is OK, but perhaps not so clear what it means for the choices other than %.
This still leaves the “Start or End or End or Start” problem. I’m beginning to think a single figure in a box whose width we can’t reduce looks odd, and that the End/Start confusion (and having to move into a second box) outweighs any benefit from two boxes being simpler to understand.
So another idea, 26b, which only has a single text box.

Note, I suggest High and Low here, because I think “Start” and “End” in a horizontal set of figures is confusing.
The other thing I am feeling is, what is the advantage in v26, v26a or v26b over the 25f idea: ?
In 25f:
- the difference between the gain and % choices is clearer
- those who want sliders won’t be offended
- you can “store” an alternative set of values if you don’t mind changing the units
Translated into our current ideas, 25f might like this (v26c):

The objections to 26c may be that:
- we have lost the “linear units” (so it may force dB default which will be worse for beginners)
- we have the Nyquist interface issue that text in the box disables the sliders (but I think Nyquist users largely accept that)?
If I personally had to decide tonight, I would go with 26c, because it lets us bring the sliders back (nor would I hesitate about making % default, but I know Steve wouldn’t agree). Maybe I will change my mind tomorrow.
Does this help? Can we agree the choice is between 26, 26a, 26b or 26c (or close equivalents of them)?
Gale