So based off the 501st CRLs and using an "average" of screenshots I've reviewed while building my own kit, the S1 cape is roughly between the mid-calf and ankle in length. The S2/BoBF cape is shorter and typically lands between the knee and mid-calf, usually closer to the knee. With that taken into account, the draped cape would be in the mid-thigh to knee range.
That being said, unless you're making your cape out of very heavy wool, having it draped shouldn't result in a noticeable weight distribution issue. Especially if your jetpack is well supported and you have the cape velcroed across the front of the flak vest like many do.
