Light companies vs voltigeurs

I'm currently writing a paper on Wellington's battalions of light companies in the Peninsula. (NOT the Light Division). I've read a few sources that try and estimate the relative strength of the French and British skirmisher screens. But they all seem critically flawed. Nominally 1 in 6 of any French infantry formation were voltiguers - but all companies were trained to skirmish so a French commander could opt to deploy all or some of his voltigeurs, or reinforce them with additional companies. A British commander could deploy his light companies (1 in 10 of his men), 5/60th, Brunswickers, Caçadores etc. But crucially it was common practice for both sets of skirmishers to have substantial reserves of up to 50% - so the numbers actually skirmishing are unknown. Also battles were seldom so neat as to have one British division, for instance, fighting one French one - attacks would often span more than one formation or just part of it. Given all this is it not very hard to make any generalisation of relative skirmisher numbers, or even to be that certain of any one instance, given that the accounts are often vague about such things?