I don't yet own Michel's Deutschland-Spezial for the DDR. My copy of Michel's ordinary Deutschland-Katalog represents the two types of this watermark as horizontal and vertical, designated X and Y, with letters 6mm and 5mm high respectively.

Is that the same as what PostmasterGS and Cupram have posted above? Or does Michel-Spezial also differentiate two types of the horizontal (X) based on letter & posthorn size?
In addition I usually find it difficult to see this watermark clearly enough to decide between the different types. Any helpful hints or techniques to try?