I'm a bit surprised you got a good cook only using one open vent but the UDS if a funny old bird and none are ever exactly the same. I cook with One open 3/4" hole and adjust from the other side of the drum with a 3/4" ball valve.
Slappin that bass like some delerious funky preist!!!
UDS, Half Pint (Mini UDS), Weber, ProQ 20, Kegrilla
*250 gallon cooker- 'The Meat Beast!!'*
British BBQ Championships
Grand Champion 2008
British BBQ Society - Southern Championship
Grand Champions 2009