I increased the number, so that the sea/river is still passable on tiny maps.
According to elexis all heights should be scaled by the map size.
For me this makes sense for hills and mountains but definitly not for waves or shores.
I'm uncertain if the sea ground height should be scaled by the map size. Conceptualy it should be treated like hills but in practice a deep see ground hurts performance and isn't noticed by players.
I'd say a map should try to preserve the feel across the different sizes. That isn't the same as blatantly scaling, in fact constructing counter examples isn't all that hard (eg, think of vertical range of ranged units). Also you already violate this supposed rule with your fix. I'd say a map author should go with the most sensible choice case by case.