If you change the first set of scales to

**(2 ** (31 - !Bits)) inverse * 0.5**

and the second set of scales to

**(2 ** (31 - !Bits)) * 2**

your example will work. (You need to do it in two steps to avoid underflow to zero when taking the inverse of 2**31.)

The asymmetry in the bit crushed 2-bit output comes in because the two's complement numbers used in computers are asymmetric: there is one more negative number than positive numbers. (You can see this in the chart of 3-bit signed integers on Wikipedia, there is a -4, but not a +4. Also, see the discussion about "Most negative number" in that same article.) When you crush down to 2-bits and then scale back up to full value, there are 4 possible results: 0.5, 0.0, -0.5, -1.0