What is the length of the slider expected in your application?
Also, which CapSense express device is being used?
If you use a common sensor in between, there may be a clash between the 2 chips, as they might scan the common segment at different time instants.
For instance, one chip may connect it to ground, while the other chip may connect it to AMUX (to scan).
So, instead of using a common sensor, you can read the raw counts (difference counts) of middle sensors (dead zone) and the adjacent sensors using host controller and calculate the centroid position.
As you have mentioned, you could also use PSoC device.