Sheet count can be right while the run is too long for that rib at that pitch. Run is slope length to the gutter, not ridge length. A 12 m ridge with a 4.6 m slope is a 4.6 m run.
This calculator warns at the generic CoP “check capacity after …” lengths: 15 m corrugate, 20 m Six Rib, 40 m Hi Five/T-Rib, 60 m placeholder tray. That is a prompt to open the NZMRM maximum-run calculator with a NIWA HIRDS rainfall, not an engineering pass.
What the warning is not
It does not model internal gutters, wall catchment onto the roof, or a local 100 mm/hr vs 150 mm/hr. Manufacturer extras still apply (Metalcraft corrugate length vs 9°). A silent green tick on a 22 m Six Rib at 4° would be the bug; you should see a check.
Length math: sheet length. Pitch gate: min cladding pitch. Split planes so a short garage does not inherit a long house run (multi-section).
If the warning fires: shorten the plane, step to a deeper profile, split sheets with a designed end detail, or change drainage. Then confirm on the current sheet and CoP drainage.