Pivot Chart - horizontal axis not showing options for bounds

I have got a horizontal axis that can hold numbers (roughly 7,5 through 18 at 0,5 intervals) based on the set filters.

I would like it to always show the 7,5 though 18 on the lower axis, even if the filtered only is applicable 10 to 12,5 for example.

Thing is, the axis options does not show bounds to set:

I've double checked to make sure my axis data is formated as numbers:

Is there something else I need to do to have this processed as a number by the chart so I can set my axis' bounds?