I think if you are in combat, without having used manoeuvres to change things, you start out at the range of the longer reach weapon - so someone with a dagger vs a naginata cannot attack the opponent because they start out at VL range, and the dagger has a reach of S (three steps less). They would have to close by two range steps, from VL to M, at which point the naginata user is two steps outside of their range and thus cannot parry. I think they can still attack, though. The dagger user is now within one range step of their dagger's range and so can attack.
Does that help, or is some other aspect still unclear?
Range steps in the English rules:
T = Touch
S = Short
M = Medium
L = Long
VL = Very Long
