Dave ,if you haven't already bought your panniers ,make a mock up out of cardboard and try several positions on your bike . You'll soon find out where you can fit them to best advantage .
Tilting them forward CAN help but I prefer to have the panniers level so that stuff doesn't rattle forward , if you only have clothing in there ,then it's not so important ,but I like to have heavy parts and similar stuff at the bottom of mine .
FWIW I don't think there is a right or wrong position , what's important is the position that works for you .
Blessed are the cracked, for they let in the light. - Spike Milligan
"When you come to a fork in the road ,take it ! When you come to a spoon in the road ,take that also ."