D38 — Adjacent copper layer as the assumed reference plane

Decision

The copper layer adjacent to a routing layer is taken as its reference plane (microstrip outside, stripline between the neighbours inside); a ground zone on it is reported as confirmation, otherwise "(assumed)"

Alternatives

Require a zone; search for the nearest plane-typed layer

Reason

KiCad boards rarely type planes as power; 2-layer boards pour GND on the far side; the report keeps the assumption visible per layer