That's only true once that particular market is open. If any bookmaker priced Man City and Real Madrid at 10/11 each to qualify on Wednesday night, there would be a deluge of big bets on Man City, until the price reached a more realistic level, such as the 2/7 currently available. That price may change over the next 32 hours, but it won't be substantially different come kick off time. Certainly there's no chance of Real Madrid going off as favourites.
The same applies to the Boro game. If the bookies have mis-priced it then money will go down on the over-priced team. But they have to make a market before they accept any bets and all of the bookies decided to install us as fairly strong favourites to progress after Sunday.