I don't have the Waterloo Game, but I'll take a guess at this looking at the picture that you provided.
If you were to "oblique" to the left that would place the regiment at a higher point on the terrain, which should increase their viewing distance.
The two Redcoat Regiments ( appear ) to be at a lower terrain level ( a depression ) which might prevent the Flags from viewing each other.
To put that another way, I think that the Flags on the British units are out of sight of the Regiment that you are controlling, which prevents your unit from seeing them.
Just My Guess!
davinci
The only true logic is that, there is no true logic!