Any of his strings canceled into close up skull pretty much.
If you jump in on someone you always want to open with the 2, 2, 1 xx close up skull because if it lands you can do a full skull carry combo. After this string follow it up with f4, 3, 4 into more up skulls. The idea is that after up skull people either have to counter poke out or jump away to escape his pressure. If poking starts to occur replace your gaps with d3 which will win every counter poke war and then continue with more f4, 3, 4 close up skull pressure.
Back on topic: Screw buffing uppercut. D1 is just way better on reaction because it turns into a 1,2 xx 1,2,2 meteor for the safe jump continued pressure. If people are stuffing your D1 then start pressing D3 to lower your hitbox. At this point if people start to wise up and use jump kicks (they wont) then I guess you will have to block like everyone else. People shouldn't have an easy time jumping on Shang though.