[rk06]

OP is talking about different things which is also mentioned in manga.

to be more precise, OP says L should use the fact that Light selects criminals only when they appear on Japanese TV.

In the manga, L did track down earliest of murders to Japan and therefore started his "world" broadcast from one region in Japan.

Light got angry at broadcast's message.and lost his cool, and fell into the trap of "world broadcast"

[throwaway314155]

I’m failing to see any distinction.

[rk06]

If my memory serves me right,L reduces it to Japan based on initial murder and then to kanto based on Live broadcast murder.