I thought to share my experience with the DPF (according to its monitoring with Carly, at least for those who use it), as well as some question marks I got and a general advice. Here it is:
1) First of all, Carly measures the soot/ash in grams, although I guess that it's just an estimation based on the sensors before and after the DPF (those measuring the pressure). It is solid and robust, as no matter when I measure it, it always gives me the same grams (i.e. it never gives me a measurement and then when I go back I have a different measurement or whatever. That said, I don't know how exactly it measures the grams inside, but it's consistent)
2) It took me a while to understand what kind of thresholds are good or bad for a MINI Cooper 1.6D DPF, but here's what I've found so far:
* 18 grams of soot is the limit where active regeneration starts happening (so that's why it hardly passes the 18g threshold). This happens even in city driving conditions, although it only gets down to 16g at most, and then up it goes again until it reaches 18g. It usually takes me about two weeks of city driving in stop/start conditions to reach this limit from say, about 3 grams.
* Usually 25 grams is where the DPF light comes on the dashboard to give you an indication to get into a highway and offload it (it has never happened to me so far)
*Between 30 and 40 grams of soot, regeneration while driving/standing is possible
* Though between 40 and 44 grams regeneration is only forced (i.e. through Carly or a different OBD2 connector) and only through driving conditions (i.e. not while standing)
* Anything from 45 grams and above it goes to limp mode.
I've never surpassed the 18.5g threshold, so I can't guarantee anything about the above limits, but that's what I've found searching around in several forums, articles etc.
3) If you force regeneration through Carly, and for the 1.6D facelift Cooper model at least, from the time it actually starts regenerating, it needs exactly 10 minutes and then it stops (no matter if it still has soot to burn). That period is actually 14 minutes from the time you actually push it to regenerate (i.e. it needs about 4 minutes of highway driving to start actually regenerating, as I pushed the button while standing right outside a highway - done that twice). You can see my first attached picture.
4) If you see the first graph, it regenerates really fast! i.e. in 10 minutes it dropped down from 18 to 7g. But... the second time I tried regenerating, it was going really slow, i.e. in 10 minutes it dropped down from 7.5g to 5.50g (it was regenerating the whole time as the "requested regeneration mode" was on in Carly). Thus, my take is that it depends on how "essential" the regeneration is, as in order to heat the DPF and burn that thing, it usually also injects diesel, so it either didn't inject diesel to save fuel, or it was just burning real slow for reasons of efficiency (?) i.e. not increasing the DPF temperature at a really high value.
5) The revs don't play so much of a role. If you see the graph no.2 that I upload here, with blue is the histogram of the revs recording in the first regeneration (where it burned the soot really quick), and with orange the revs of my second regeneration (where it was burning the soot real slow). In the former case, the revs were usually between 2500 and 2700 and occasionally around the 3000 mark, whereas in the second regeneration, the revs were more around the 3000 to 3250 mark. Moreover the engine was already at temperature, as well as the DPF, as the second regeneration was enabled while I went to a roundabout and back on the same highway, thus the temperature was already up from the previous trip.
6) As you can see, passive regeneration after the requested one did not do anything (although I'm not sure if this is mainly because a forced regen was requested before), but it roughly kept the soot at the same level for the time driving the car.
That said, my first general advice would be don't get too frustrated with your DPF, but monitor that maybe once a week, and if it's near the 18g threshold, just take it for a ride and have a coffee at a city near you that involves at least 15 miles of highway and you'll be fine
My second general advice would be, while Carly is nice in itself, the app costs about 50£ and the adaptor another 62£ and it doesn't show you the % of soot in the DPF. Mike has proposed the AUTOCOM which, among other things, has some really powerful tools including the DPF. So if you have a Windows laptop, and you don't want to spare 100+ quid for Carly, this is your option to go! (Thanks a lot Mike!)
P.S. For those wondering, the first trip was 15 miles of (normal to a bit busy traffic conditions) highway, and then a roundabout and back (another 15 miles).