Size of opening doesn’t matter at all. It’s visual trickery for your brain. All DRS does is reduce the drag of the actuated flap as much as it can. You can do this by flattening it, or as it’s now possible, by flipping it upside down.
Drag reduction eventually is dictated by the final resting position of the actuated flap and the gap it makes with the rest of the rear wing makes no difference at all.
The maximum amount of drag you can reduce via DRS is equal to the drag of the actuated flap and it depends on that flap’s surface area.

