look, folks - just because you CAN submit more than one, doesn't mean that you SHOULD.
there's an old saying in football for teams that use two quarterbacks and rotate them. the fact that they have 2 starting quarterbacks is really an admission that they have no starting quarterbacks. the fact that you are pumping out 5 - 10 proposals probably means that, far from having 5 - 10 good ideas, you really don't have any.
why don't you craft ONE proposal and try to knock their socks off that way, instead of going for the shotgun approach. trust me, if your fifth proposal is "NINJAWORLD", save the postage and don't even send it.