It seems like some folks are looking at this like daily limits – which do have an effect on parent/subdecks. But it should be treated like parameters and nearly everything else in Options – whatever is assigned to the subdeck the card is actually in is what controls.
90% – from the preset, since no deck-specific DR has been set.
70% – from its own preset.
No. And no switch, or anything else. (That’s not what the “limits start from top” switch does anyway.)