I try to keep my loss 90% or better. Kettle cold knockout/BBT fill. To get a better idea of my loss point I have calibrated some beer tube and installed it on a fermentor to gauge my FV fill and pre-filter volumes.
Calibration simply with a 5gl bucket and a shapie. Note buckets are NOT 5gal at the rim- I in turn calibrated the bucket with a 2 quart measured pitcher. The connection point to the FV can be with a TC hose barb or even just clamp to your perlick - its not a permanent connection.
In the end Ive found thet my filtering is good and most loss occures in the trub pile and transfer to FV, then in dumping and cropping yeast.
your results may vary...