planetfall and Arathorn both are correct.
PF, the civopedia is incorrect in 1.13. That version was verified by testing to have distance corruption determined by distance to nearest palace (including FP), and the civopedia didn't match. This discrepancy was noted and in subsequent discussion and patches, the 'code' was the one determined to be correct. So Arathorn's comments are true, both for v1.13 (and v1.15 and likely beyond)
"- Distance is calculated from nearest capital building for distance corruption
- Rank is still determined by distance from the one true capital for rank corruption
- The FP has some special rank or coding to keep its corruption minimal
- OCN is bumped way up by the FP to mask the effect of the rank corruption if the FP is "near" the capital"
Regarding the last two notes:
* FP city corruption is capped at 30% max corruption for one thing
* OCN boost is currently around 3/7 (37.5%) but is subject to tweaking
Also:
* Max city corruption is likely to drop from 95% to 90%, and also likely that a courthouse would decrease that *max* corruption further, but this is subject to testing.
So that's the current status anyway. (Subject to change... they do call it 'beta' for a reason)
Charis