Martin, how had the blade been sharpened before you got it? If it was sharpened in the factory only then it likely was not sharp enough and got dull quickly. Stropping alone would not be of much help then.

I do not think that the position/angle of the strop really matters as long as
* you can strop with a reasonable speed
* you keep the strop taut
* you do not apply much pressure
* you do not lift the spine while stropping

Send your Dovo to a honemeister. It will thank you. Your face will be grateful.