Lael, I have Beersmith set to 20 litres into the fermenter and without tilting my BM it will leave 5 litres to trub.
In that 5 litres there is still a lot of good beer so depending on hop additions I usually leave about 2.5 to 3 litres behind after tilting the BM. This is after a settling period of generally around 45 mins.
I am not looking to extract every last drop as I basically only keg these days and I only need enough to fill a 19 l Corny from each brew.