I agree that the preferred route is fresh yeast, but a starter that is new with a dose of the old slurry is really awfully similar to a starter of new yeast that has finished and settled out within the starter. But, regardless, I would pitch it at high krausen for either approach. Look into an Shaken not Stirred starter and pitch it at high Krausen and I bet you will get some downward movement in the gravity. Just a guess - nothing science based in that.