It's old unit ?
Strange...
I have difficulties to understand bit main business model...
Aside from still poor yields the chips have rather wide range of performance not only batch to batch but even as far as between dies from the same wafer. That variation is why Bitmain and others all use auto-tune to eek out the best performance from the chips.
Have a top end of 13.5 just means things were a bit off at their foundry TSMC for this batch.