The optimal frequency with which to send out your letters and your ROR will be something unique to your market.

I would be interested to see how the post frequency is growing monthly or some such.

Although, this would differ from county to county, but the indicator assumed that influences in the frequency and speed of transactions between buyer and seller to be the fundamental basis of property taxation based from speculative land valuation formula.  

Did get one call that said "your letter is distasteful"So what is everyone doing in their direct mailings...what is the frequency...when should I send the second round?

There may be a scanner frequency that is used by your fire dept. or they may list recent fires.

What is your method/frequency for following up with these near misses?

The issue is frequency is a complete crap shoot and timing of payments is immediate.

This means multiple points of contact and frequency. 

And for many who have cash they get hooked to the passive nature of the business and to the returns that over time will usually out perform rental properties.Once folks have been through the rental cycle and realize how tough it is to be a landlord they start looking at lending its a natural progression.. of course many have a combination of both.. but I have seen it happen with great frequencies over the years.. my clients selling off rentals to put into notes.

But a new market is a new world and you need to mitigate risk by pulsing experts, agents, investors, business owners, renters in an area to vet your analysis as much as possible, and use online resources to check crime rates, school system strength, foreclosure  frequency etc.