Not a Parker but in a previous life I shot and ducks out to 40 yards with Hevi Steel (no longer available) with a Benelli M-2. As J.B. stated above, bigger shot patterns tighter than small shot through the same choke. The same is true for hardness of shot.
I shoot Nice Shot #2 through .030" in Parker 10 gauges and pit down Canada Geese at 60+ yards. Sometimes I put down more than one
Nice Shot is 3 times as hard as hardened lead shot. ITX is 10 times as hard as lead and should be magic through a skeet choke.
Now, let's talk about choke which is a measure of the performance of a load through a certain barrel constriction. In a modern 12 gauge Skeet "choke" is the result of factory target load shot through a barrel constriction of .005". This is of course an average since each load will pattern slightly (or in some cases greatly) different through each individual barrel with the same constriction.