Generating downforce with a chimney

Having in mind that Malaysia is one of the hottest venues of the year and therefore requiring lots of cooling, one may ask himself why Williams is not opening up their chimney more instead of having the exhaust area decreased. The basic reasoning behind this is the aerodynamic effect of the chimney itself, which by its shape forms a Bernouilli wing. It creates downforce as the air underneath moves faster than above. It is however a questionable approach which Williams is using for several years now. They lack performance and are about the only team to have such big chimneys. In top of that, it are the only chimneys which blow out air at the sides instead of upwards.