I'm not familiar with those engines, but normally, the DPF is nearer the front of the car to get it hot. They're usually the next box after the cat. They're the only box that has small bore pipes coming off them (they're pressure sensors so that they can tell when they need a regen). My guess is that it would be round about where tthe gear lever is or slightly ahead of that. If the OP can't easily get underneath, possibly find a cooperative teenager (if there is such a thing!) and ask it to take a video on their mobile phone with the phone taped to a stick that can be pushed under the car, bomb-disposal squad style.
