Long story short, managed with a workaround, still not 100% suitable.
Question: Do you think rear mounts with standoffs are strong enough for long tours on shaky roads with ca. 15 kilos/33 lbs of gear/food/water?

Now the long version, with photos:

First of all, I have managed to lower the existing rack by flipping the extensions upside down. Now it sits ca. 6cm lower, just as I'd do it in the best case, see the picture below:



However such a workaround created another problem, there is barely enough of heel clearance now. It's ridable, but i do hit the panniers every once in a while. It would be Ok for a smaller person, but (eh, like always) not for me.

I do need a lot of heel clearance, i have 205mm long cranks and wear shoes size 51 EUR/16 US.

The idea to move the rack rearwards was the first one i've thought of, seems very logical. In fact, if there were no upper mounts i'd just do it without hesitation.

But the upper mounts seem to be much stronger than the lower ones in the rear. The seatstays contact area of the upper braze-ons is at least twice as large.

Upper mounts:



Lower mounts:



Upper mounts seem to be much stronger, I can put sufficiently longer bolt through it.

Now I need your opinion, is the rear mount strong enough to hold a lot of luggage on shaky roads? Won't standoffs increase the leverage and the chance of mounts failure?
I see many people praising their steel frames for being able to repair the cracked rack mounts in the field. But I just want to avoid that if i have a chance.

PS. I have no chance to customize the rack right now, except for DIYing new extension plates. Got instruments and material some time ago (I saw the problem coming) but sooo little time..