Kindly note that you need to follow the guidelines as per the newly updated English version of the document which has answers to your questions. The guidelines in the Japanese version of the document is old and needs update.
Please note the following:
1. The shield spread should be within 1 cm as given in the updated design guide.
Refer: http://www.cypress.com/file/46366/download (MBR3 Capsense Design Guide) - Layout Guidelines for Liquid Tolerance section. Pg no 41
2. There is nothing as such like minimum spread for the shield. The minimum area for shield electrode can be the area remaining on the board after implementing the sensor (ie <1 cm)
We don't recommend any PCB ground plane in the same layer of that of the shield or underneath the shield. You need to leave it empty (beyond 1cm spread).
Refer http://www.cypress.com/file/41076/download (Getting started with Capsense guide), Shield Electrode Construction for Liquid Tolerance section, Pg no 86.
I hope this answers your questions!
Thank you very much.