Adaptive Data Rate on LoRa-E5

I’m connecting a LoRa E5 module to TTN with ADR turned on. This works really nicely and I can see the spreading factor being reduced almost immediately when the gateway is close (actually in the same room). My question is: what happens when the gateway drops off the network and I need to rely on one further away? The module should have a backoff strategy for increasing the spreading factor if it gets no response to an ACK request or Link Check Request, but there’s nothing documented to say how that works.

I could change the data rate manually to back off faster, but that seems to disable ADR, even though the module reports that it’s still operational.

Does anyone know any more about this?