Hi!
Yes, its what you say.
French regular units have more men per element than british units (200 vs 120) and tropes the marine has also 200 men but less hits (8 instead of 10 IIRC).
So 20 hits on a British stacks will be shown as a lot less casualties that on a French stack.
As the men per hit are just "flavor" numbres this is not a real bug (the combat result calculatiosn are done on hits and the result is OK).
But definetely it sometimes look strange (those damned redcoats are really resilient!

)
This is one of the reasons why element sizes should be as homogeneous between different sides and unit types as possible.
Cheers!