not 100% sure as this is something I've covered yet but wouldnt it just be a case of affinities,
so as said in the first one an oil soluble drug and a fatty base, the drug has a high affinity for the base it is within so little release. In an exam you could introduce log P values here ( organic/ aqueous)
Compared to say the water soluble drug in a fatty base, it would have a low affinity for the base and thus rapid release.
Not sure if Im going along the right lines... if this is the kind of answer you are wanting PM me and I can go into more detail