Perhaps it was to do with the down-sizing and streamlining of the nose. Does the DB engine still have an oil sump or reservoir at the bottom? If it is removed and replaced by oil injection there is no need for a sump thus removing weight and bulk from the engine. It would possibly need some sort of reservoir/cooler but this could be positioned further back and behind the engine as it appears to do so. Doing this along with the raising of the crankshaft/gears nearer the centre line would enable some streamlining due to the reduction in engine size.
Edit: Bit more info here
'Daimler-Benz DB 600 series engines - one of those designs that turned out to be right from the very start... Inverted mounting provided better visibility, lower center of gravity, and improved maintenance access. In the Bf 109, a cannon was mounted between the engine banks and fired through a propeller hub. The DB-601A in the Bf 109E, used fuel injection instead of a carburetor, a great asset in combat since the engine did not cut out under negative g' forces. This engine was also used in some Heinkel 111s and license-built versions in the Macchi MC.202 Folgore and several Japanese aircraft.'
Answering my own question, the picture on the page shows that there is a flat oil reservoir, situated at the bottom of the engine inbetween the valve mechanism covers.