Walt you have to look at each pond as a system. Elevation , water supply (ground water or springs) , potential for high wind , turnover history , plankton status (fertile or not) , temps , depths [thermal refuge] , DOs , etc all play a part in the TShad choice. Cost and risk are also factors to consider. The closer one gets to the edge (in this case lower lethal temp range limits line) the more important each variable becomes and the less room for error and thus the increase in risk.

My I-40 comment is an approximate north-south area range(like your latitudes) but is easier for most to understand.

I note your comment about correcting LMB crowded ponds " the only way it would take years is if ineffective methods were used ". Ineffective methods are very widespread as is misinformation and misjudgment on this subject among most pond owners. No doubt most knowledgeable PB members could do the job correctly provided they did not have an unintended consequences event. Those are very common when trying to balance between the 2 possible unmanaged situations ( BG crowded vs. LMB crowded). The next issue of PB has some thought provoking info on this exact unintended consequence situation.