Since Distinctive ring has a very special ring cadence composition, you might be able to distinguish lines by changing the ring validation time on LINE port.
The related setting would be: Physical Interface --> LINE port --> Ring Detection --> RingValidationTime
What "RingValidationTime" does is to examine the minimum time period of ring burst, and it provides a range of 100 ms to 1024 ms.
Let's say you have two lines, one has cadence: 2 seconds ON, 4 seconds OFF, and the other one has cadence: 0.8 seconds ON + 0.8 seconds OFF + 0.8 seconds ON + 8 seconds off. If you set "RingValidationTime" to 1024 ms, then, only the first line is able to ring your OBi unit, and the second line will fail to ring your OBi unit because it does not have long enough ring burst. If you set "RingValidationTime" to 512 ms, then, incoming call on either line will ring your OBi unit.
So the best you can do is to change "RingValidationTime" configuration on your units (say 256 ms on one unit, 1024 ms on the other unit), then, you have one unit rings for the line with long ring bursts, and the other unit rings for both lines.