That's the good news about empire garments. The bad news is that most larger-sized empire sweaters are often upsized versions of "standard-sized" garments that increase the length and width of the sweater - but don't move the waistline.
A perfect example is Hey Teach, designed by Hélène Rush and published in the Knitty. This free pattern, much beloved and made by more than 2000 people on Ravelry, features a lace bodice and stockinette skirt.
It's a cute design. But Hey Teach has a real fit problem for larger women: the bodice below the armholes is always exactly the same length regardless of the size, and the length from the waist to the hem doesn't change either.
Take a look at the schematic and you'll see what I mean. The pattern calls for a different armhole depth depending on size. But the area beneath the armhole does not vary whether you're making the 32.5-inch size or the 55-inch size.
However, on an ample woman, that bodice ends smack dab at the nipple line and the hemline ends in the middle of the stomach. The photo below shows what I'm talking about. Unmodified, Hey Teach's bodice ends below the bust of the thinner woman and across the bust of the larger one. Similarly, the hemline hits the smaller woman at the hip and the larger woman at her belly.
This doesn't mean that larger women shouldn't make Hey Teach or similar designs. It just means that mods will lead to a better fit. If I were going to make this, I'd measure to figure out exactly where the empire waist should begin, making sure that the ribbing hit a couple of inches below my bust.
Hey Teach is knit from the bottom up for eight inches. Then you knit about 1.5 inches of ribbing and switch to the lace pattern. The pattern tells you to knit until the piece measures 13 inches and then start the sleeve shaping. If I were making this sweater, I'd lengthen the stockinette portion of the skirt by an inch or two, add the ribbing, and then knit the lace section until it was deep enough to cover the space between my armhole and empire waist - about nine or ten inches instead of the four inches called for in the pattern. Mind you, this is for my body - your mileage will vary.
These considerations apply to empire waists that are designed to fall below the bustline. Some sweaters are designed for that line to hit at the nipple line, such as Marly Bird's Sweetheart Tunic.
And some, like the ubiquitous February Lady Sweater, are designed to hit above the bustline.
Regardless, the moral of this story is: when you make an empire sweater, make sure you figure out exactly where the waistline should hit on your body and modify the sweater accordingly. You'll get a much better, more becoming fit if you do. Ensure that your sweater fits your body as the designer originally intended - even if they don't provide you with the specific directions to do so.