The slider-module is not only looking at the position your finger is on, but on its neighbours as well. So it is able to give you more than one value for each slider-segment.
With that kind of variation it would be pointless to have more than 4 elements in the slider.
Some notes from design manual -
In most cases the default value of 8-bit is appropriate. However, in designs with high signal levels due to thin overlays
or large sensor areas 16–bit resolution should be selected. Because sliders calculate finger position using relative
signal levels of adjacent sensors, saturation causes non-smooth operation and 16-bit resolution may be required.
Widget Resolution: Select 8-bits unless you are using a slider and the signal is saturating due to thin overlay or
large sensor area, then select 16-bits
7.4.1 Opamp Output Pins
The opamp outputs are directly connected to P0, P0, P3, and P3. If these pins are used for CapSense, the
opamps become unusable. These pins have higher CP because they are directly connected to opamp outputs.
Therefore, these four pins should not be used for CapSense. If you must use these pins, they should be used for
buttons and should not be used as sliders or touch pads. Also, the traces for these pins should be short to help