• 78.7 baseline — 0.6 × season 73.5 (15 gm) + 0.4 × last 10 86.4
• −3.5 opponent leak — they concede 1613.3/game vs a 1687.8 league average
• at this ground: too thin to count (3 gm) — shown, adds nothing
• −16.9 wet forecast — averages 61.8 in the wet (9 gm)
• vs them: averages 82.0 over 2 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.