In my efforts I saw that with SF7 I have 200m range to have safe delivery. So dense GW in my view is every 200m. I agree with you, this is very rare. But with GW’s every 1km, you can transmit with SF10 and occasionally with SF7/8/9.
I experienced an exception to 200m “rule”. A very “tall” GW is missing many transmissions even in <200 meters. Maybe noisy environment or something else.
I repeat: You can use SF10 and switch to SF7/8/9 if you are close to a GW or in “white zone”. Also in my efforts I saw very rare cases that GW’s that are 7-10km away are catching my signal (currently testing with SF9). So, again in those areas you can switch to SF7-9. I even will try to use FSK when close to GW. This is something unstested. Also you can transmit only when necessary, not every X time.
The TTN fair usage policy is easy to follow. Don’t transmit with SF11, SF12 and don’t exceed the 30secs limit.
My payload is 7 bytes and I transmit: location, position (stand, fall), gps fix (on/off), battery level (4 states), direction (accuracy 24 degrees) and speed (accuracy according to needs), quality of GPS fix. If the device has the same position (50meters). I trasmitt only one byte with the above info minus location but with full battery info (0-100%)
Just re-checked my numbers: (SF: Success)
SF12: 71%
SF11: untested (covid-19 quarantines not helpful)
SF10: 68%
SF9: 62%
SF8: 41%
SF7: Untested (covid-19 quarantines not helpful #2)
Those are not scientific measurements, just traveling 9km’s with differents SF’s with the tracker. The tracker was transmitting in RANDOM / unpredictable times.