Thanks for thinking along, it's very helpful. So it does have active PFC after all...
By experimentation, I had already confirmed that R1..R4 are indeed the current sense resistors.
I found that I need to remove one 6R80 and the 9R10 to get close to the desired light output, so I can modify these units without any cost.
The result is a 6.8 W unit with still more than the current unit's light output @ 8.5 W.
I took a photo with 4 units side by side to view the comparison on screen (my eyes see less difference than the camera).
From left to right:
1) New unit, driver modified to 170 mA.
2) New unit, driver modified to 223 mA.
3) New unit, driver not modified, 300 mA.
4) For reference the current unit, not modified (note: 2700 K, the others are 3000 K).
Tech.data:
1) CC 170 mA @ 32.8 V; 5.6 W; mains consumption: 6.8 W (PF 0.89), about 82% efficient.
2) CC 223 mA @ 33.1 V; 7.4 W; mains consumption: 8.9 W (PF 0.93), about 83% effiicient.
3) CC 300 mA @ 33.5 V; 10.1 W; mains consumption: 11.6 W (PF 0.95), about 87% efficient.
4) Ref. unit: CC 350 mA @ 21.5 V; 7.5 W; mains consumption: 8.5 W (PF 0.76), about 88% efficient.
Tonight I will compare the different units and choose which mod. I will apply.
Edit: with 170 mA current flowing, the LED panel doesn't even get warm, so a multiple of the specified 35,000 hours should be possible. I don't know if the driver will do that too, though...
The usual suspects in the limiting of the driver's lifetime will most likely be the electrolytics. Though Aishi may not be the most well known brand, in lighting products they almost seem to be a given. About 90% of the CFLs and LED-lamps/-drivers I tore down (from whatever brand) used Aishi. Their failure rate also seems quite good, on par with the big boys.