According to TTN with EU868 band, do I need to change any of the radios setting to improve coverage?
As far as I read, 125 KHz is better in terms of coverage if the payload is very small. Also according to the setting page all radios support multi SF data rate, so no need to make it fixed.
You are indeed on the right path, this is pretty much as good as it gets. As for the SF, yes they are all MSF, so no need to tamper with this as well.
To be honest this is not that useful (at least according to me) for the EU868 band, seems it is very constraint, see if it were the US915, than there are a lot of things to be done and played with as you have a lot more channels, thus freedom.
Still feel free to experiment and perhaps share some of that hard earned knowledge
Changing the gateway’s radio settings is unlikely to make things any better, and quite possible to make them not work at all. You’re best leaving everything at defaults.
The actual decision of what spreading factor to use is made by the node firmware, though if ADR is activated in a node configuration, then the applicable network server will try to advise the node what spreading factor is best for the conditions.
TL;DR leave the radio configuration alone, what matters is the node firmware and the node configuration in the network server, be that either the internal one or an external server in the cloud.