Dear Morteza,
The lead field matrix should have elements in the order of magnitude of 1e-6 , so every signal with a unit amplitude should not give an output in the order of 1e3 as you now have. I don't know why you use the conv function, since it is a direct multiplication with your source signal (Measurement = LF*Sources).
Why the effect of scout 2 is bigger I wouldn't know to be honest, as far as I know brainstorm uses every vertex in a scout to simulate so that might lead to a difference.
Kind regards,
Steven