The population of the city doesn’t really equate to support, though. The built up conurbation of Nottingham is larger than Coventry, but the city is actually smaller by about 40,000. People quoting Coventry at 325k aren’t using the latest ONS data - it’s in excess of 370k, now. The catchment area is key, and there are likely a lot more people around Nottinghamshire who support Forest than there are people around Warwickshire supporting Coventry. This wouldn‘t represent a million people though as has been suggested, there are only roughly 830,000 people in Nottinghamshire county which includes the city; and because of boundary bleed to the west of the county, some of those will be Derby fans or follow Notts County (or not follow football at all, or maybe ((but less lilkely than around Cov)) support a prem team).
Coventry also has a far more transient and diverse population that wouldn’t necessarily consider Coventry ‘their city’ and a large Irish community who in the main support Man Utd, Liverpool, Arsenal or Celtic and a large asian community who without generalising too much would likely pick a prem team to follow . Historically, Coventry has one of the most active local Saturday football leagues in the country and this also impacts attendance. Our realistic support has never matched its potential and that is proven when it comes to big matches and away days when fans do turn up in number.