# Adjust spacing between specific rows with \xymatrix

I have the following diagram:

$\xymatrix @!=1pc { & Z \ar@{.>}[d]^{\exists!h} \ar@/_1.2pc/[ddl]_{p'} \ar@/^1.2pc/[ddr]^{q'} & \\ & X \times_S Y \ar[dl]_p\ar[dr]^q & \\ X \ar[dr]_f & & Y \ar[dl]^g \\ & S & }$

which looks like this:

I want to decrease the spacing between the second and third rows. I know about @R=xpc, but that will decrease the spacing between the first and second rows as well.

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$\xymatrix @C=1pc @R=.5pc{ & Z \ar@{.>}[dd]^{\exists!h} \ar@/_.6pc/[dddl]_{p'} \ar@/^.6pc/[dddr]^{q'} & \\ \\ & X \times_S Y \ar[dl]_-p\ar[dr]^-q & \\ X \ar[ddr]_f & & Y \ar[ddl]^g \\ \\ & S & }$