This is exactly where things get interesting. If species are not carrying the spell, how does that which is carrying the spell react to the elements of the world? When the caster's voice is quiet, magic realizes the caster wants a short range; where there is a wall, magic is somehow is constrained by the physical form of a boundary. Can rego magic of any other form than Vim constitute a boundary for magic itself? I should think not. In this sense a ReIm ward should not be able to reduce the distance of a voice range spell as the magic is reacting to the volume of the caster not to the volume of the sound.
The magic of voice range must originate in the vocal chords and mouth cavity of the caster, or at least somehow be connected to what is going on there. Once it gets it's marching orders, the spell is not going to be hindered by anything other than that which effects magic itself (parma, vim wards, counter spells).