Very good question! By reading the RFC, it seems like like the goal is to bring DROP up to TIN levels - the other way around does not make sense, if the goal is to incentivise people to invest in the DROP tranche.
Thus suggesting we should be incentivising the senior (DROP) more heavily going forward as this is the current pain point and will likely remain so going forward.
But maybe @thespaceacatjr can clarify this.