I've started using a wool felt wad saturated with patch lube between the powder and the patched ball. I don't see much difference in accuracy, but it prevents blown and smouldering patches (which were a problem before), and it allows a lot more shots without wiping the bore.
I have sort of a double boiler system that allows me to melt my preferred bullet lube in its tin. Once it's melted, I drop in wads or patches one at a time. They soak up lube like a sponge almost immediately. I lift them out with tweezers and lay 'em on a clean cookie sheet to cool. Once the have cooled, I put them in a tin of their own. Excess lube on the cookie sheet can be scraped off with a spatula and put back in the lube tin.
I've stopped buying pre-lubed patches. For me, a tallow and beeswax mix, or just tallow, does everything I need it to do, and I honestly believe it keeps better than the commercial Wonderful Lubes and Bullet Butters. I think these commercial lubes start to break down after some time has elapsed. The pre-lubed patches then seem weakened, and fouling appears to accumulate more quickly. If you get dry patches and wads and apply the lubricant yourself, you can do small batches with no difficulty, just enough for a day's shooting. This works well for me.
Getting back to the original question, I would agree that an over powder wad is a good practice. Walter Cline described using a felt wad in loading at least one of his rifles in The Muzzle-Loading Rifle, Then and Now, so it is not a new idea. It may not be necessary for every rifle, but it is something simple you can try, and it is a logical intervention if you are getting burnt or blown patches.
Best regards,
Notchy Bob