problem with BS818 and TS04 capacitive touch sensors

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hi I'm working on a 12 key capacitive touch keypad that uses BS818 for 8 of the keys and TS04 for the rest. my problem is that when i use a 3 mm light guide on top of the touch pad and a 2 mm plastic on top of that the sensitivity is not good. but when i change the plastic to 3 mm glass the sensitivity is OK. i used the schematics provided by the datasheet of these chips except i removed the sensitivity capacitors for maximum sensitivity. i can't upload my whole PCB but i attached a part of PCB and schematic.what might be the problem here?