A consistent approach to particle shifting in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" id="d1e1386" altimg="si213.gif"><mml:mi>δ</mml:mi></mml:math>-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" id="d1e1391" altimg="si6.gif"><mml:mi mathvariant="bold-italic">Plus</mml:mi></mml:math>-SPH model