Reflections of Low bit rate signal and High bit rate signal
The magnitude of the reflection can't be more than 100%. And no line is loss free. After some time, the ring caused by the reflection will die away due to losses. 

If the bit period is long, the ring will (more likely) have died away before the middle of the bit period, which is the ideal time to sample the bit.

If the bit period is short, the ring may still be ongoing at the middle of the bit period, and thus cause an error in sampling the bit correctly.