[maple_leaf_eh]

There is a slim but good book by Prof Terry Copp on 5 Inf Bde that speaks to your question (and others). < amazon.ca/The-Brigade-Terry-Copp/dp/0811734226 >

Don't forget the regiments were not 100% deployed. The fighting companies were kept topped up with men from the echelons. The army left a lot of administration and logistics to the regiments. Consequently the troops forward knew who was behind them too.

A second consideration has to be the ratio of LOB or Left Out of Battle. Not every single rifleman, section commander or staff officer went in to battle. A fairly significant percentage were kept out of combat intentionally. These were needed as replacements and as a means of cycling tired or slightly over-stressed troops out and back into the companies.