taken note lora tracker thank you 4db extra transmit power on battery use
are each sf low not also 0.5 of transmit time?
What does that mean ?
is sf7 not 0.5 of sf8 airtime?
About, but not exactly.
Use the Semtech LoRa calculator to check.
On air time doesnât directly impact distance - indeed longer range comes from fact that the higher SFâs have more availability (time) for any given SFâs message âsymbolsâ to be seen. Shorter on air time means you might dodge a bursty interferer but you are not then on air for longer to allow symbol detection and correlation to happen against a general noise floor vs a bursty noise floor, swings and roundabouts! 
Whilst doubling with each step in SF there is a ladder effect and package sizes will generate a payload and SF induced staircase effect on timings - you need to look into the details but can see the kind of behaviour here (bottom of page) https://avbentem.github.io/airtime-calculator/ttn/eu868/13
As a general rule LoRa is able to recover data if <~ half of a symbol is lost, so quite rugged/resilient. Though actual perfromance is in part dependent on the nature of the interfererâs modulation schemeâŚ
OK so for example 10dBm on 434Mhz will go around as far as 14dBm on 868Mhz and it appears the 868mhz is using more battery power.
But on 868Mhz you could cut the TX back to 10dBm, so same power consumption as the 434Mhz, but then use a gain antenna to get around the same range as the 434Mhz setup.
The question I guess we all want to know the answer to is what is the real reason for wanting a custom 434Mhz setup ?
A few dB power more or less donât matter. Much more important is an undisturbed Fresnel Zone between gateway and node.