The histogram panel of the FITS viewer is a bit confusing to me

1) When I click 'Hide saturation Spike', the histogram curves, that reach a frequency (y-axis) of 3E6 for my image, are cut to a bit higher than 1.5E6.
What the rationale of this cut is?
Is not 'saturation' more related to the intensity parameter (x-axis) ?
Is the 'Hide saturation Spike' switch affecting the image ? (I press 'Apply' and I do not see any change).

2) The x-axis scale (Intensity) of the histogram goes up to 4095. I guess this is because my Nikon camera image is 12bits (2**12 == 4096).
This Intensity max value can be modified for each of the three colors R,G and B.
I can set them for example to 2867, 2048 and 3071 (R, G and B, respectively). Then, if I untick 'Hide Saturation Spike', they are automagically changed to 2826, 2007 and 3030...
What the rationale of this is?

3) The range of the x-axis of the histogram graph can be set to any value between -INF and +INF (actually I only got to see up to -6E67 +6E67).
Are negative numbers to be expected for Intensity?

Forgive me if these are too silly questions. I was used to the APT histogram to control the exposure of my images. This one seems a bit more convoluted and I haven't been able to find any documentation to help me.

=1= Unfortunately, the feature 'Hide saturation Spike' is now gone in the current version 3.6.2. @jasem is it coming back?
=3= According to the manual, the viewer is capable of displaying float-based imagerey, that could include negative numbers.
"""
Support for 8, 16, 32, IEEE-32, and IEEE-64 bits formats.
"""