I am reading a paper and there is some computation of RHom of sheaves that I don't understand. I hope this is the right place to ask.
It is this paper, example 3.10 , page 25
arxiv.org/pdf/1005.1517v4.pdf
The first RHom equality.  Why does the result come shifted by the codimension?
(In the paper they denote the diagonal of $M\times M$ by $\Delta$.)
How does one begin to compute RHoms of such sheaves in general? will deRahm resolution work?

Thanks !