Well, it's not absolute, but generally that way.
I have seen people post pics on forums before where they said the meat was nasty tasting and the smoke was thick. The pics posted showed how they added fuel to the firebox. I remember one in particular in a smoker similar to the ones in the pic earlier on this thread, where the charcoal and wood filled over 3/4 of the total volume of the firebox.
It is difficult to imagine that much fuel burning cleanly in such a constrained environment, let alone sucking in enough air through the intakes.
I have a small offset similar to yours, and I use the Minion method every time. The first thing I did was raise the charcoal grates so there was about 6 inches clearance below, which also gave me more surface area for charcoal (double sweet). Yours may already be this way, but if not do yourself a favor and make this change. I took a perforated stainless steel paper plate holder which I bought from Ace Hardware and set it up in the hole between my firebox and cooker to keep flames from being able to leap in to the cooker. I have seen others do this same thing with a perforated pizza pan. With this in place, I would put the lit coals on the charcoal grate against that "baffle", or looking at it another way I put them on the grate and shoved them as close to the cooker chamber as i could with a fireplace shovel. Then I backfilled to the intakes with unlit charcoal and let the fire burn backwards toward the air intakes. I get consistent 90 minute burn periods with Royal Oak lump doing this. I would not add a really thick layer, just a good layer with decent coverage, probably about 3 inches thick or so. I would put 4 to 6 chunks (depending on size) on top of these coals evenly scattered from front to back and side to side. When it was time to refuel, I would shove all the remaining lit coals to the side nearest the cooking chamber, and backfill the same as before and put on some more wood chunks as before. I ran about 240-270 this way, with 90 minutes between refueling like clockwork.
Larger offset have larger and deeper fireoxes, and some have charcoal baskets designed for a snaking Minion method type burn, and they can go quite a while without refueling. For the smaller offsets though, you're gonna have to refuel.