When he hits you with a block, he hits you harder. Height isn't the end all and be all to power. With a 400 pound weight differential, the Ogre and Giant are NOT the same size when all dimensions and factors are considered. Monster OD&D 1e 2e 3.5e (HD/DMG/Height) -- ...
Each level has a pattern bearing fixed points with jumps and giant zombies that exist to block your path. If you fail to kill these giants in time, they will kick you into the landslide. The jumps, however, should help you strategize when you want to get past certain parts of a level....