1) The Pokeradar exclusive Pokemon can only be found in strongly-rustling grass.
2) If a Pokemon encountered via the Pokeradar, defeating or catching it will cause the grass to rustle again.
3) If the same Pokemon is encountered in the newly rustling grass, the chain counter increases by 1. Else, the chain breaks.
4) If the strongly-rustling grass rustled even more, it'd seem as if sparkles are coming off of it. Perhaps these sparkles represent a very strong Pokemon?
5) Capturing a Pokemon is more likely to yield the same Pokemon species appearing in the newly-rustling grass rather than KOing it.
6) The longer the chain, the more likely it is for the grass to rustle super-strongly.
7) At most four tiles can rustle when the Pokeradar is used.
8) Encountering Pokemon in tiles further  from himself seems to have better odds of encountering the same Pokemon again.