[Sephiroth]

That's exactly what you need to bring the power level down to the ideal 0 dBmv.

BTW you can check your pre-HDU power level by disconnecting the HDU from the incoming line, attaching the SH to that incoming line (hopefully you have the old splitter) and doing the upstream/downstream measurements and sepeed tests again.

Of course you have to be sure that your speed tests are not being conducted at times when you could expect doffeent results.