The only way to create the back splatter effect of a contact shot, is by (you guessed it), a contact shot.
The ballistics expert, Malcolm Fletcher, did not prove or establish that any blood had actually got inside the silencer by the process of back spatter, or back splatter, or drawback! All he did was postulate by providing an explanation as to how that blood could have got there, there was actually no physical proof that the blood in question had got there by those means!