Symbols indicating dynamics are all relative!  A *f* in one context might sound completely different than in another context.  This means that you can use the symbols in a flexible way to convey your intent.  If you have a sequence of crescendos, where each one lands at a louder level than the one before, then you could have them land at *p, mp, mf* or at *mp, mf, f*.  An experienced musician will interpret *f* according to the context.