I always steep my blacks twice. I used to steep them once, steeping about 1 gram of leaves for 3-5 minutes. Then I tried taking twice the amount of leaves (2g) and steeping it for half the time, twice. It made quite a difference for me. My black teas taste much more lively and clear this way, the first as well as the second steeping, while the total leaf/water ratio in the end is exactly the same. The whole taste profile becomes more pronounced by the higher leaf/water ratio, while the shorter steepings prevent the bad sides of oversteeping, such as bitterness, astringency and overall saturation of taste. I do the same with green teas now, while for oolong I usually go for a much higher leaf/water ratio and many more, shorter steepings.
You could call it the 2/2/2 technique: 2 grams of tea, 2 minutes, 2 steepings. I don't understand how this works physically, but I guess the extraction process all doesn't work so linearly as you would think.
Re: Steeping blacks twice
You have travelled half the distance on the path from Western style brewing to Gongfu brewing, go all the way and do a proper gongfu 