Best played as ...

[NicolasBourbaki]

Hi, in RBOTR (and probably in other games too) can someone explain why some scenarios are "intented to be played as" Allied or as French ? 

And why some other scenarios are supposed to be HTH only ? What if I play a HTH in solo ?

Does it means the AI is scripted, ie. not a true AI ?

For example, I would like to play Valmy as French but all scenarios are either for HTH or "intented to be played as Allied". 
And in the solo scenario, all FR units are fixed in the early battle. Not sure if they unblock later ...

Thanks