It says scatter it D6 inches.. if you roll a "hit" on the scatter does it not move at all? When scattering purple sun it says to use the little arrow on the bullseye, but it doesn't specify for Pit of Shades.
I'd think using the little arrow on the 'hit' marker is the exception, not the rule. A war machine that rolls a 'hit' does not scatter -unless using indirect fire, in which case it specifically says to use the little arrow. Purple Sun specifically says to use the little arrow, but Pit of Shades does not; thus I'd say a 'hit' lands right on target for it.
in our club we play that it can be a direct hit as it doesnt say to use the small arrow. But without the direct hit the spell would be much worse imo.