If they truly are less transparent, change the transparency of every pixel on the surface to the same value (I'm afraid I don't know how to do this in XNA). If they only seem less transparent, try drawing your sprites onto the surface completely opaquely (so one will completely overwrite the other), then again change the transparency of the surface as a whole.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.