When you use the Pokeradar is DPPt it generates 4 zones around the character. Zone 1 is always one tile adjacent to the player so is the closest to you, while zone 4 is furthest away.

Zone 1 has a 28% chance of continuing your chain

Zone 2 has a 48% chance of continuing your chain

Zone 3 has a 68% chance of continuing your chain

and Zone 4 has an 88% chance of continuing your chain

If my math is correct then this means that Zone 1 has a 72% chance of breaking your chain, Zone 2 has a 52% chance, Zone 3 has a 32% chance, and Zone 4 has a 12% chance.

Source

As for catching it as opposed to defeating it, according to Bulbapedia it does increases the odds of a chain to continue, but only for the patches that shake immediately after the battle ends. Unfortunately though, I couldn't find the exact numbers for this.