What is the exact encirclement bonus?
Unavailable from the checked sources. Publishing a percentage would be an unsupported guess.
Battle mechanics
Official feature confirmation plus timestamped encirclement context and diagnostics.
Updated

The creator description names encirclements and supply. It does not publish range, throughput, penalty, attrition or encirclement-bonus formulas in the checked metadata.
France footage repeatedly identifies encirclements during war at jQxwDL3wkv4@03:04-03:36, @05:46-05:58 and @09:13-10:12. This verifies live use of the concept, not a numeric modifier.
Before blaming a template, preserve the visible front, surrounding provinces, current supply indicators, participating units and battle result. A screenshot without map context cannot establish an encirclement.
An encirclement describes map isolation; supply is a separate named system. The checked sources do not prove that every isolated unit has the same supply state or penalty.
No exact supply threshold, attrition rate, recovery timing or encirclement combat bonus is published here. A community percentage requires repeatable current-version tests before inclusion.
Front-line behavior is especially version-sensitive because drawable front lines are named as a future roadmap item. Recheck after control changes, then use /divisions/ and /guides/beginner/ for the wider workflow.
FAQ
Unavailable from the checked sources. Publishing a percentage would be an unsupported guess.