If you are on the brim of fire(fighting Measure).... You have to step in to perform your lateral strikes. Maintaining proper distance makes you step in... which gives me time to intercept....or evade and counter. If you are inside.... Then the JKD person is left with intercepting. Straight line attacks have less distance to travel. Hence they are faster given if both opponents has the same speed. The quickest path between two points is straight. Sometimes that line is covered so you have to go lateral like you are saying. So summary. If I am on the brim of fire.... and aware and not sleeping... You need to attack to hit me.... I intercept... or evade and counter. Inside.... I have to intercept. Esp. if I am tooo deep. Take two people standing face to face. same hand speed. One throws a hook... one throws a straight punch. Both launch at the same time... Who lands first? Of course this doesn't always happen. But it shows how a person with slower hands can stop hit someone throwing a hook.