• 1.8 baseline — 0.6 × season 1.8 (17 gm) + 0.4 × last 10 1.8
• −0.2 opponent leak — they concede 4.7/game vs a 5.1 league average
• at this ground: too thin to count (1 gm) — shown, adds nothing
• vs them: averages 1.8 over 4 games — evidence, never summed

Derived, not measured — plain arithmetic over his real games, shown in full. Adjustments can overlap (a game at this ground can also be a wet one); they add simply, and this note is the admission.