From park attendance loss of 1 person there is losses to revenue so the percentage does not actually matter. All it might possibly do is say if its really important to offer or its not as important to offer.
Flip side the discount someone gets is minimal at best for Disney in grand scheme of all revenue extracted from a family. Using October as an example below.
Baseline ticket price: $700 (10 days hopper ticket) or $625 (10 day base ticket)
DVC AP: $720 or $620 Renewal
AP: $1270 or $1070 Renewal
The only cost you really care about is the difference between DVC AP vs AP which would be a loss of $450-$550 per person ($50/day). This then is a negotiation point from DVC to cover some of the cost and Parks looking to provide a discount to a high affinity group to draw them in so they are eating dinner at higher priced restaurants vs the surrounding area.
How much day tickets are are less consequential since when people stay less they will be on day tickets anyways and if they did buy an AP when day tickets would have been less Disey would make more money by offering a discount that backfires on the guest. If they stayed more if it was approaching the $1270 or $1070 AP costs they would be getting the out of state AP anyways and not paying for 2/3/4 separate tickets.
I think you can likely zero out any difference from people who buy 3 separate tickets and would have saved money on AP vs those who bought an AP and actually would have saved by buying individual tickets.
Except that is a Parks discussion not a should DVC get a discount discussion. DVC has point limits on blue cards to both increase sales but also to limit the number of future members so they can afford to pay Parks for the discounts/events that they negotiate.
Also if Parks didn't want to provide a AP discount there is likely some other discount they would work out with DVC as they have shown through the years there will be some type of ticket discount for DVC members so they obviously feel something needs to be offered or there would be a loss of revenue.
I just think this is way to much in depth when discussing a ticket/AP discount for DVC. There isn't extensive losses when you consider Disney already has the capacity just sitting empty otherwise anyways. Flip side there could be the potential gains.