Interesting. Your research is providing some improved perspective. Let's see:
1. Lower frequencies have better propagation characteristics, but
2. those lower frequencies sacrifice more db's to get to a compact size, unless
3. cost goes up
Is that right?
If that is true, then is it all just a wash, or does any one particular ISM band standout as best suited for both range and compact size and low cost? Is it 433Mhz or 850-950Mhz (or possibly an even higher frequency?).