Not sure where you get the >4, >4, 16, 5.
Urs rolls last turn against TOUCH AC were 1 (Failed hit), 18(Hit, but then failed trip), 16(followed by successful trip), and then non-trip attacks. His Trip attack this turn was a 5.
Thats 1, 18, 16, 5 for his last for touch AC/trip attacks.
ALSO...