Keep in mind condos are challenging with limits on frequency and duration of tenancies, HOA approval of tenants and often the condo fees kill cash flow. 

Channel, frequency, firmware, software, security settings, noise in the environment, something as simple as moving furniture around can impact coverage. 

You only have their word as to the frequency of flooding and you have no idea why it’s flooding now.

And of course there are all the real estate sales stats like DOM, closing/listing price ratio, frequency of multiple offers/bidding wars, etc.

So the simple of it the way I see it is if I have control of a property that after all relevant and real costs are accounted for on a monthly basis allows for a $220mo Cashflow then I can hit my goal by repeating that as well as increasing my frequency of purchasing to the tune described above.  

But you have to be good at finding deals someplace other than the courthouse steps to bring consistency, frequency, and volume to your opp funnel.

Is there any difference in the frequency or extent of the problem within different types of property or based on their size or their floor plans or their geographic locations?

Clearly, the septic system is part of that.You'll get a large range of opinions regarding the frequency of required cleaning.  

I know that no matter what list or what frequency I mail I will need to be consistent.

You want a targeted segment with much more frequency (hit them ads more often).