Coolant Capacity Sprint Gt 1050

I realise that this has been covered before so please excuse is this is going over old ground. I have just completed a Coolant change on my Sprint GT. Prior to filling with new Coolant I removed the Radiator "Vent" screw. I them slowly added Coolant via the Radiator filler cap. After about 1/2 to 3/4 of a litre Coolant began to flow from the Cylinder Block drain hole at which time I replaced the drain screw. I continued filling until the Radiator was full with Coolant flowing from the Radiator Vent hole. The Vent Screw was then replaced. I shook the bike from side to side as best I could and squeezed the Coolant hoses. A few bubbles did escape from the Radiator filler hole. I added Coolant to the Expansion Tank max line. All of this has only used 2 Litres of Coolant. As posted before the Haynes Manual gives a capacity of 2.8 Litres !!. My Triumph Owners Handbook says 2.3 Litres. I ran the engine until the Fan cut in. After cooling down the level in the Radiator is full to the top.
Is it possible that I have trapped air which is why I can't get the extra 0.3 of a litre in ?
Any help and advice much appreciated.
Thanks.