I won't be so smug as to say I have considered EVERY possible configuration and mechanism but I have spent a fair bit of time thinking through possible mechanisms.
Volume of fire is of course one way to look at it, the same effect can be achieved by providing Modifier factors for certain troop types or considering certain troops under certain circumstances as superior.
R2E classes British in line as VETERAN for shooting purposes which gives them between +1 and +3 extra shooting dice before applying punitive modifiers.
We also need to be a little careful about the 'efficacy' of musketry in general. Most casualties in the Napoleonic Wars were caused by artillery.
Don't quite know what you want to hear from me.. did I consider? YES
Whilst I would like to think that any set of rules I offer up is somewhat grounded in logic and history.. it is all to play games with models. TMoE was written to give a fast, fun, entry level Naps game for brigade level action with some crossover mechanics introducing character figures. An easy way to build a bridge to fantasy players or youngsters overfaced by the'BIG PERIOD'.
Hope this helps...
Anyway, I have NEVER been a subscriber to the 'uber' quality of the British infantry which makes them invincible under all circumstances in the way that some people also view the Imperial Guard. They were beaten and that is no disgrace just fact. Circumstances usually dictate outcomes. Wargaming has long been very Anglo centric and so this reputation of the British has been layered over several generations. I think we need to get the Brits in proportion.. they rarely were the 'sole' component of any army but often through our own biased history grab disproportionate amounts of the collective glory... it all started way back with the cult of Marlborough I believe...