I am flying from just about anywhere in Europe to ATL the week of June 17 with a return the week of Sept 9 or 16. I would prefer to be RT in/out of the same city.

I am able to fly from any of these cities:
LHR
CDG
MAN
DUB
GVA
Milan
MUC
FRA
BRU
ATH
IST

I cannot seem to score this golden 100k mile ticket when the calendar shows low miles, even looking at Economy through the seach instead of Business. Any suggestions? Am I better off playing around with the search engine or having a phone agent help?