We did picnic with a wheelchair and were in blue where there are some benches - maybe 3 tiers up? Kind of far back but not bad, and pretty close to center ( next section to our right was center ). There weren't many people in that section so we didn't have any heads in front of us -- only about 3 or 4 people deep at the worst that evening ( last Friday).
There was another blue wheelchair area even further back - make sure you get the dining one ( a nice CM saw me headed for the other but noticed my picnic bag and set us right)