Not knowing exactly what your are trying for:
1) For complete bleaching and sepia toning, make the print (generally, and depending on the paper and sulfide/NaOH ratio you use) slightly flatter and denser. For fiber paper, 1/2 or 1 grade less contrast and don't compensate for drydown, this usually works.
2) If you want the harder shadows and sepia highlights, you really have to do a light selenium tone first to lock in the blacks, then bleach and sepia tone. Great look, but the process is quite a bit longer for fiber because of the hypoclear and wash after the selenium.
3) If you try partial bleaching, that is to say grabbing the print before it gets to the shadows, it still has affected the shadows. You will see this even if you finish with selenium.
And yes, if you bleach to comlpletion and sepia tone to completion the selenium will do nothing. Playing around with full bleach and partial sepia redevelopment followed by selenium results in varying degrees of rusty red-brown.
In any event, density is always lost with bleaching.