Yep - as you say you need to cover all the ingredients in liquid so pack the hard stuff down and fill all the gaps then cover with stock,sauce or water. Before eating I empty the slow cooker and either boil the cr-p out of the liquid to reduce it or make a roux and add the liquid bit by bit.
I did chinese style pork last night with 5 spice,fresh ginger and garlic,onions, soy sauce, sweet chilli dipping sauce and tomatoes. Overcooked it though as the meat fell off the ribs each time I picked it up to have a nibble.
( Oh - I have taken to marinate all meat ( cockerall pork and steweing beef) for 12 hours or more before I put it in the slow cooker - fuller taste if making coq au vin or beef in red wine).