• 21.8 baseline — his last 10 games; only 1 this season, too few to blend
• −2.3 opponent leak — they concede 31.6/game vs a 35.3 league average
• +4.3 at this ground — averages 26.1 there (39 gm)
• +4.6 wet forecast — averages 26.4 in the wet (10 gm)
• vs them: averages 25.3 over 6 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.