It is remarkable that in 2200 miles of driving both uphill and down hill it would deplete the 1/4 battery indication to zero and would always regenerate on the down slope to 1/4 but never ever above 1/4. Now if indeed it is capable of regenerating past 1/4 charge it is a remarkable coincidence that this never happened on a 2200 mile trip. On long down hills 1/4 battery was seen but never above that even when there was a good amount of down hill to complete.
Looks like a software design error to me. If the 1/4 is being exceeded behind the scenes then that is a display error if not ( I suspect it never in HEV mode ever charges the EV section of the battery) then it is a major design error.
It's not a software flaw, it's designed that way intentionally. When the battery is depleted to close to 0%, it uses nearly 100% power from the ICE, and none from the battery, so it can build up some energy back into the battery. Once the battery charges to 25%, it starts to aggressively use the battery again, because it no longer needs to build a charge. So whqat you'll see on the battery meter is that it climbs from 0-25% fairly quickly, but then gets "stuck" at 25% because it's not working so hard to charge the battery anymore.
It isn't remarkable at all that you didn't see the meter go above 25% on your 2200 miles drive, I didn't see mine go above 25% for the first 3000 miles either, and I only have seen it twice ever now, coming down VERY tall, steep, winding mountain roads.
Your ICE's energy is more efficiently spent propelling the car than charging the battery, so the car (smartly) directs all its energy to the wheels when it decides the battery has "enough" charge.
As mentioned several times earlier, it IS possible to charge past 25% while driving, but it's rare and requires very specific circumstances. Namely, VERY long, fairly steep downhill sections (several miles) where you are going less than about 40-50mph, riding the regenerative braking the whole way and not accelerating at all. And you're not going to see the meter climb that fast - expect about 1 mile added to the meter for every 3-5 miles of riding the brakes coming down a mountain. The most charge I ever got was +5 miles, and that was after about 30-40 minutes of nonstop regenerative braking.
Above about 50mph, the car won't be using very much regenerative braking at all, because wind resistance alone will be keeping the car from gaining any momentum.
Trust me, as much as we'd all love to see that meter climb to 100% on long drives, it's more efficient for the system to be doing what it's doing.