... Mis-align between the silicide block and one or other side of the resistor will always be in one direction. This changes the effective interface resistance left vs right or whatever. In addition to this, there is also an implant mask between the silicide block and the end cap in the direction of the contacts. This also causes a mismatch one side vs the other. Both of these can act against one another to enhance the mis-match. In addition to this, even if the heavy implant on the end caps is done at zero degrees, no implanter is exactly zero degrees. So there is an additional mis-match. ...