I tested everything possible :
- the recommanded A2/B2 (per user manual) : fail
- Only A1, A2, B1 or B2 : fail (B2 recommanded if only one stick)
- A1/B1 : fail
- A1/A2 : fail
- A1/A2/B1/B2 (4 sticks) :fail
Only B1/B2 works (no matter what stick drom the two kits I use).
And belive me, testing all those combinations is a real pain in the ***, I have to remove the venitrad each time... Only for this I regret not to have bought a AIO water cooling system !
If I understood well, in order to have the dual channel active you MUST (I can be a lawyer too !

) use A2/B2 (end of daisy chain to close it) if you have only 2 sticks (and of course A1+A2+B1+B2 if you have 4 sticks).
Obviously A slos are either angry at me or in vacation. More probably out of order.
That's not a problem if you turn yoursel into a lawyer, I have a good legal protection insurance !!!