1. Connect the bottom layer hatch to the shield.
"When there is a grounded hatch fill or a trace then, when a liquid droplet falls on the touch surface, it may cause sensor false triggers. Even if there is a shield electrode in between the sensor and ground, the effect of the shield electrode will be totally masked out and sensors may false trigger.
Follow these guidelines to implement the shield electrode in two-layer and four-layer PCBs:
Top layer: Hatch fill with 7-mil trace and 45-mil grid (25 percent fill). Hatch fill should be connected to the driven-shield signal.
Bottom layer: Hatch fill with 7-mil trace and 70-mil grid (17 percent fill). Hatch fill should be connected to the driven-shield signal. "
You can find this information in the section Layout Guidelines for Liquid Tolerance (Pg no 110) of PSoC 4 Capsense design guide.
2. We recommend a minimum air gap of 1.6 mm.