According to Wellington's General Orders on the subject the light companies of each brigade would form a converged light battalion for the march, and this might be formed at the front, flanks or rear of the brigade depending on tactical circumstances. The second General Order (for the Waterloo Campaign) specifically mentions marches whereas the former (for the Peninsula) does not, however I would assume that the same principle of forming light battalions during marches was followed in both campaigns. Detail of General Orders is below:

Extract from General Order issued at Coimbra on 4 May 1809

3. The light infantry companies belonging to, and the riflemen attached to each brigade of infantry, are to be formed together, on the left of the brigade, under the command of a Field Officer or Captain of light infantry of the brigade, to be fixed upon by the Officer who commands it. Upon all occasions, in which the brigade may be formed in line, or in column, when the brigade shall be formed for the purpose of opposing an enemy, the light infantry companies and riflemen will be of course in the front, flanks, or rear, according to the circumstances of the ground, and the nature of the operation to be performed. On all other occasions, the light infantry companies are to be considered as attached to their battalions, with which they are to be quartered or encamped, and solely under the command of the Commanding Officer of the battalion to which they belong.

Extract from General Order issued at Bruxells on 9 May 1815

1. The light infantry companies belonging to each brigade of infantry, are to act together as a battalion of light infantry, under the command of a field officer or captain, to be selected for the occasion by the General Officer commanding the brigade, upon all occasions on which the brigade may be formed in line or column, whether for a march, or to oppose the enemy.

2. On all other occasions, the light infantry companies are to be considered as attached to their battalions, with which they are to be quartered or encamped, and solely under the command of the commanding officer of the battalion to which they belong.

3. The Commander of the Forces wishes that some of the light infantry battalions of each brigade should be practiced in the manoeuvres of the light infantry, and if possible in firing at a mark.

Rod