If you really want to control your ESD environment it doesn't stop with ESD mats and straps. The aerospace industry has a high standard for ESD. This document from JPL covers alot of it. I'll cover some of the basics.
1) Materials can be an ESD hazard, paper, clothing, plastic,furniture and other materials can generate a voltage that can be hazardous to electronics. Make sure all materials are ESD safe.
2) ESD areas are tightly controlled, they are checked periodically to ensure they are grounded, and there is proper impedance from the strap to earth ground.
3) Humidity and other environmental factors need to be controlled.
4) Lab personnel should wear ESD jackets, this helps keep you and your clothing at a decent potential. You might be wearing a strap, but your clothes could be generating a few thousand volts.
5) Access is controlled, you don't want stupid people walking up to your board and zapping it.
There is more but that covers the basics, something to think about. To answer your question in case you skimmed it. Yes you can have a potential on one side of you. During one ESD training I had, they mentioned that a few thousand volts exist on a person from head to toe. IF you have an ESD jacket it turns you into a faraday cage.
If you can't find the link try looking for JPL-D1348_Rev_F