Is it capacity or wattage or both? I’ve charged to 100 before long drives, but by the time I’m out of my little town I’m usually at like 98 percent so it’s not a real worry. Then onto the freeway and within a 1/2 hour I’m way way down. I thought the issue was bringing a two ton vehicle down to a stop quickly Would overwhelm the charging system in the car. But I could be wrong.
To add to @quagmire response, it is also a factor of if your battery is at a warm enough temperature to take max regen. If you drive off without preconditioning, the vehicle may reduce regen to protect the battery, especially in the winter.
In the winter NYC metroplex winters, if I leave work before my scheduled preconditioning by GPS location (and forget to manually remotely trigger preconditioning), I will get reduced regen for the first few miles until the battery warms up. This will be starting out at around 60% battery (leaving in the morning at 80%, driving 26 miles and running sentry mode all day).
With the feature turned on, it is seamless to the driver, the only way you would know is if you look at the power consumption bar on the infotainment system. You will see either no green, or a portion that is green followed by grey on the negative side.
If it didn't "Blend Regen" when this happens you would have a different experience than when under full regen. This is not the best user experience, and to me can be dangerous as it changes One Pedal Driving. This isn't a Tesla thing, this is an EV thing as many manufacturers deploy this, some may do it without the driver even knowing it exists.