How many of Hertz's rates are flat rates (same rate regardless of location, demand, etc.) versus percentage-off rates?

Among the usable-by-retail-customer rates, it seems like most Hertz CDPs offer a percentage off, although the percentage doesn't seem to be consistent, necessitating trying a gazillion different CDPs to find the one that offers the best rate.

The small business CDPs also seem to be a percentage off (at least it's certainly not a flat rate), but even though they claim "up to 20% off," I've seen rates less than half using a small-business CDP a friend signed up for.

I actually have yet to find a flat-rate CDP, but I haven't messed with some of the codes published on FT and other places that are for companies I don't work for ("State of FL," etc.--those kind). Are those typically flat-rate accounts, or do even large corporations get a percentage off? Does Hertz offer a choice between a flat-rate and a percentage-off discount when negotiating with companies?

Most of my experience is with Dollar and Thrifty, which offers either percentage-off promo codes (5-10% at the most) or flat-rate CD numbers (i.e. Dollar's BJ5013 CD number, the BJ's Wholesale Club discount, which is a flat-rate account).

The BJ's one in particular seems odd to offer as a flat rate. Flat rates make sense for corporations that want to be able to plan for rental cars to be a consistent expense. They may be willing to pay more than retail rate in some cases (and less than retail rate in other cases, of course) for the benefit of always knowing exactly how much to budget for rental car expenses. But offering a flat-rate plan to retail customers seems odd. If and when the local retail rate is less than the BJ's flat rate, the retail customer will just book without the BJ's code, making it useless. And when the BJ's rate is lower (sometimes significantly so) than the local retail rate, there's a reason the retail rate is so high--demand is high and supply is dwindling, in which case it seems against Dollar's interest to offer the BJ's rate.

On the other hand, at least Dollar's options are transparent--either you're using a promo code that's a consistent 5 or 10% off the retail rate (although sometimes retail rates are loaded that are non-discountable, in which case adding the promo code can actually cause the rate to go up), or you're using a CD number that is a flat rate. With Hertz, you never know how much a given CDP is going to take off, so you have to try them all. I find that searching for rates with Dollar (and Thrifty) is a lot less cumbersome, although with enough work, you can get Hertz rates down into the neighborhood of Dollar and Thrifty rates (and sometimes beat the total price with creative use of PC codes).