A shot in the head and then a slide into an enemy always sets up a heavy melee, so does a quick shot and then a slide. So yh if you do the the frontal heavy melee, which is officially called a coup de grace, it gives u 7 secs instead of 5, this is the other way to go for high scores if u dont like countering or a counter isnt strong enough to kill an enemy like it often is the case fighting Javo. Usually ud have to weaken a Javo to be able to kill him with a counter and the weakening of course takes some time so doing it this way basically gives the same results but needs less effort.
If you are in stage with zombies though simply countering will give u higher scores though since a counter usually kills a zombie at full health with the power counter if not without it.