Hi... I love ropes, and have three ropes. In my humble opinion, I absolutely feel the length of the rope needs to match where it lands on your body. That is key. A 30" rope on a very tall and large woman would not look good.
I am 5' 2", and my ropes are 34", 38", and 52". These are all odd lengths as you can see, and I had them customized to fit my frame. I wanted a long ropey, swinging look, and when I went to Mikimoto to try the 30" and 32", it didnt "swing" enough for me. That's when you can buy a strand and then add extra inches. The sales person was very helpful and helped make the lengths work. I thought for sure being ony 5' 2", the 30" would be perfect. They did look good, but they did not look great and did not "swing" (hard to explain, but swinging is the whole point of wearing ropes... think 1920s).
I like to wear my 34" and 38" together, and that spacing between the two land perfectly for where my torso it. Then, I also wear my 34" and 52" very often and it evokes a very casual swingy look.
So my suggestion is... try on some ropes and look at a full length mirror and see where it lands on you. It matters if you are small or big busted, if you have a thin or thick waist, etc.
Just my humble opinion. I hope this was helpful.