Most Likely Redundant But...

FYI: If the front end is higher than the rear, you won't be able to get all 3.8 quarts back into the car. The fill plug is next to the half-shaft towards the firewall. So any excess ATF would simply drain out, until you can get the fill plug back into it.
Now if your slightly nose down, you should be able to get all 3.8 quarts into it, because the fill port is slight higher than it should be - if the car was level.
I've got a good slope in my driveway and the car is pretty much level when the front tires is on rhino ramps. I think it was slightly nose down, since I was able to get about a cup more into it than I drained out. No issues after about 30K miles ago.

Hope this helps....

PS, Those plugs are pretty tight when you first crack them - use a breaker bar and don't strip them...

 

Answered you here:

2016 Prius transmission fluid change | PriusChat

For the "car should be level" factor, Toyota never mentions that, but they spec that the fluid level should be at most level with with lip of the fill hole, and as much as 8mm lower. The presumption is that they're not talking to DIY'rs using ramps or floor jack; they're assuming the car was raised with a lift. So you want to achieve level, one way or another.

Then when you fill, getting the level right is by simply filling till it starts coming back out.

My pref is to raise the front with a floor jack, settle onto safety stands, then repeat at the rear. Roughly level is all you're aiming for. Safety stands are cheap, and virtually necessity for safely working under the car. An alternative could be to run the front up on ramps, then jack up the rear, and leave the jack in place. That's sketchy though, I would raise the rear and settled onto a pair of safety stands. Also, whenever practical I'll push a large wooden block (tree trunk section) under, before I get under.

See also the transaxle fluid change link in my signature; it's gen 3 specific, but mostly applicable. (on a phone turn it landscape to see signatures)

 

at 44k, i wouldn't bother