By 'midrange' do you mean:
* cruising at medium RPMs (steady RPM)?
* accelerating through medium RPMs?
or
* throttle open 1/2 way at steady cruise?
* throttle open 1/2 way during acceleration?

Start with venturi/choke size. 30mm is good on twin-carb setups (one barrel per engine cylinder) for max power maybe at 4000 RPM with a 2-liter engine. It will rev higher, but make max power way down low. With a single sidedraft each barrel feeds two cylinders - it is jetted the same way but the carburetor sizing differs. 30mm single is good for maybe 5000 RPM with a 2-liter.

In DCOE/DCOM series, the main jet should start at 4 x venturi size. For 30mm venturis, start with 120 Main Jets (for DGV (32/36) the guidleines are totally different)

The Air Correction Jet should be 1.25 to 1.50 of the Main Jets. For 120 main jet, start with 165 Air Jets.

That much is easy. The trickier part, for which tuning to the engine is called for, is the transitions.
* When accelerating the pump jet and duration is the main factor, I have no idea what the guidelines are for the DCOM.
* Transition between idle circuit and cruise circuit is controlled by the Emulsion Tubes and Idle Jets with minor effect of air correction jets. Do not attempt to fudge this by raising or lowering the float level. The Float Level should be set to the Weber specifications before any other tuning is done.