I'm trying to create a quota tabulator that will adjust a quota value by .5 point for every full point increased or decreased AND will limit the total increase or decrease by a value of 3 points.
This is the formula that I've come up with so far:
=if(or(or(C2-B2<=0+1),or(C2-B2>=0+1)),(mround((C2-B2)*0.5+B2,0.5)),B2)
This formula correctly adjusts the quota when the value is decreased. 
It does not correctly adjust the quota when the value is increased. 
Regarding the limit by which a value is increased or decreased regardless of the score that is entered, and referencing the pictures above, the updated quota should not be able to be more than 21 points or less than 15 points. I have no idea how to do that.
My problem is that I don't understand what I'm doing so I don't know what is making the formula calculate decreasing values correctly but increasing values incorrectly. And, again, I don't even know where to begin to make the formula limit the value's increase or decrease. Any help will be greatly appreciated.