New TOTO valve closes too fast?

Just got a new Toto Clayton installed. It seems to me that the red valve (don't know it's real name), which opens when you pull the handle, closes too fast. It doesn't let the tank completely drain, but just slams shut as soon as you let go of the handle. So, the longer you hold the handle, the more water in the flush...

Is this right? Is there an adjustment I can make somewhere?

Thanks,

C

Most 1.6 gallon toilets only use some of the water in the tank.

This is normal.

Performance is a little better when the water is stacked in the tank. The higher it drops from, the more speed.

If you had five or 3.5 gallon toilets before, you would have emptied most of the tank.