TTIG fixed to SF7 with LMIC & Arduino Uno

Well, I bought a TTIG. Set it up. Everything works. Made a simple test node with Arduino + RFM95, using old LMIC library version 1.5.1. OTAA works. As in my town it is the only GW and no other users are around, I wanted to play with it a little. So I made a weatherproof housing for TTIG and put it on the roof.
I took my node, and walked around little bit. For some reason all the joins and other data transfers are made always at SF7BW125. Either it is SF7BW125 or nothing. So I thought my node library is rather limited, but in other city the same node achieved even SF10BW125.
So, it must be the GW that is limiting SF.
Any idea what configuration bit must be changed? Or TTIG is somehow limited to only SF7?

No, it is a full standards compliant LoRaWAN gateway. It has no intelligence beyond dropping packets that fail CRC. It just hears radio waves and if they are waggling up & down the right way, demodulates, checks the CRC and if it passes, sends it to the LNS. Only the LNS can request a change of DR.

Unlike the ancient LMIC version which may not be able to respond to the MAC commands as expected. Or it may have something set or not set that is stopping ADR from working. Or you just have a really flat town. Probably all three.

Regarding “only GW and no other users” which is only true after you’ve asked everyone in person in a radius of 15km of your location. Gateways don’t have to be made public nor do devices have to be regularly transmitting, the community asks that everyone that hosts a gateway acts like someone else may have a really good use case that relies on coverage.