G'day Concretedust
I've tried techniques similar to this with a couple of armies. It can work well, although it's tricky to manage and there are drawbacks.
Let me explain with a couple of examples.
I've used the Sub-Roman British with commands containing massed Sp (I), and reserves consisting of Cv and LH. A typical command consisted of 24 Sp, plus 4 Cv, 2 Ps, 1 LH, a general and 2 baggage, for a total of 24 Morale Equivalents. The command thus became Disheartened when losses reached 6.5 Morale Equivalents and broke when losses reached 8.5 Morale Equivalents. With the Sp fighting in three ranks, I could afford to lose the entire front rank of Sp, and even quite a few of the second rank, before the command became disheartened, and theoretically the command would still be intact if the entire two front ranks were destroyed. In one game I faced a Cham army, and pretty much every element in my opponent's front rank had a quick kill against the Sp. Despite taking heavy casualties, my Sp had the advantage of high combat factors, and eventually I got lucky on the dice. My opponent had few reserves, and once there were a couple of holes in his line, my Sp started wrapping the flanks of enemy elements, and his losses increased dramatically. In the end I won the game with only one disheartened command, even though I lost more than half the Sp in the army.
In a similar vein, my Early Byzantine army includes an infantry command consisting of 8 Bd (I), 4 Ps (O), a Bd (I) general, and 2 regular baggage, for a total of 18ME. That command breaks only after the loss of 7 Bd (assuming I keep the Ps and general out of harm's way).
Another example I'm looking at involves the Komnenan Byzantines, with commands of 0.5ME Bw (I) up front, backed by 2ME Bd (S) Varangians. A command with 8 Bw, 2 Bd, a general and 2 baggage could lose all of the Bw and not even be disheartened.
Another way of playing with these rules includes the use of 0ME troops like Expendables, or the simple Polybian Roman army with Bd (O) backed up by Sp (S) and regular baggage.
The general rule is to design commands to lead with low ME troops, and pack the reserve line with high ME troops, generals, regular baggage, and maybe even Baggage (S). How well it works depends on how well the low ME troops fight and how quickly they die. The latter in turn partly depends on what army you're facing. For example, any army leading with Bw (I) in two ranks will be in trouble against an opponent with Wb or decent quality mounted.
Anyway, that's my experience. Your experiences may differ.