Hi,
it's logical if the calue is an angle in degree. it goes from 0 to 360 and if you go positive, it goes up, but you go directly from 0 to 360 on the the other side, maxing out to your positive clamp value.
for this, you should turn your rig 90° so that you clamp your angle between 80 and 100 for a 20° range.
Does that make sense?
Bye,
Jean