I don't know why people are paying attention to this indicator despite being confident that it's useless. I disagree with the latter. I've been compiling daily stats on Batt.Kapa.max, and its (monthly) averages seem to be quite close to the SOH calculated via the trip computer data. I've been following Batt.Ladung as well, and this one is all over the place. It matches Batt.Kapa only at 100% SOC, and in all other cases severely underestimates the current "capacity" of the pack.
My understanding of Batt.Kapa is that it provides some estimate by the BMS of the total kWh amount that was able to sneak into the battery during the latest charging session (the BMS extrapolates in case the charging was stopped before 100% SOC). Then this very amount is being used while driving - no more than this really, if the BMS "thinks" that's the max in there. So, when you approach a depletion of this amount, the BMS signals you with XX range remaining warnings and then shuts down the system. If this hypothesis is true, Batt.Kapa is the true SOH at any given moment. At least the SOH I'd be interested in - 'cos I'd like to use some kWh from the pack to drive, and that's the amount I can use.
Why it varies so much for so many people is another question. From the data I have so far, its variability was quite modest during summer, but then it started falling rapidly with the decrease of ambient temperature (October-November). This makes sense - the battery's capacity decreases in cold conditions. Batt.Kapa may vary also depending on the state of cell balance, and due to the normal (or abnormal) degradation of the pack. Maybe there are other factors at play, I don't know.
Now, this hypothesis may be thrown away based on your case - you have a 12.5 kWh Batt.Kapa and a decent range of 75 miles. In case Batt.Kapa is fair in the assessment of the true capacity of the pack, you efficiency should be about 6 miles/kWh, quite a stretch. So, I don't know
Other reported low Batt.Kapa values (both here and on FB group threads) matched well with the GOM based and actual range, so your case is unique and thus very interesting. But if I were in the US, I'd certainly try to talk to the dealer on this basis asking them to assess the pack (they run some procedure, I understand), and replace it under warranty in case it's below 70% (12.5 kWh means it's at 66% SOH, if we were to believe the Batt.Kapa here).