I’ve tried to draw up an image of the throttle situation. I had to massage the figures a little in Excel to get the visual representation correct so I will only included the graph.
With the TQ6+ throttle, whose raw axis is from +16383 to -16383, mapped to +1 to -1 in SPAD, the idle detent on the throttle rests at around -9100.
Below is an image showing on the left the raw axis, in the middle a rough guess of what SWS are doing regarding beta(?), and on the right what my TQ6+ is doing.
My idle detent is now about half reverse thrust. From memory, full reverse is -25, and I believe the mouse over tooltip reports -15. My placement of the SWS beta range is total guesswork, not backed up by evidence. 
Idle on my TQ6+ is now quite far into reverse thrust, while actual idle is some way into the blue area, with no detent to identify it by feel.
Perhaps this could be massaged a little by playing around with the axis mapping, so instead of +1/-1, maybe +1.5/-1? Essentially expanding the forward component until “0” sits at my physical idle detent. I have no idea whether that is possible without actually trying it, but it makes sense in my head at least.