[Imp]

This map does have level zero terrain as well?
Ask as hill heights needed are those between min & max terrain height.

Messing with vertical scale has issues, namely blind hexes produced.
The game produces blind hexes based on the height per level set by the game, increasing it means it should block less hexes if looking over lower terrain.

You are wrong regarding 4 height bumps they do block LOS but not by much because its a bump. Even do so from a slightly higher hill so long as the bump is not close enough to see over.

Put a unit on a level 1 hill and make some level 4 bumps 20 odd hexes away they will block LOS to the hex behind them.
If the bumps are closer guessing 8 or less hexes they will not block anything as close enough to see over.

From the same level view can change radically over a bump if other hinderance terrain comes into play.
View can also change due to visibility level with this type of feature, hinderance terrain combinations, smoke etc block LOS far quicker in low visibility compared to high.
Put some high grass on a flat map position units to see across 3 or 4 and adjust the visibility to see this.
This type of terrain can be great for units with vision aids as it might be enough for them to see more.