Mxnet-SSD: How to choose aspect ratios and sizes of default box?

[Chida15]

I have got the real sizes and aspect ratios of the objects, how can I use them in the mxnet?
Assuming:
num_classes = 6
width: 29.55, 41.71, 72.41, 82.82, 96.68, 114.57
height: 32.47, 49.55, 62.53, 76.10, 88.38, 103.33
ratio:0.39, 0.83, 1.08, 1.48, 1.83, 2.32

I set the sizes and ratios just like this and I use the function MultiBoxPrior to get the default box,
however, I just can't get the right result!
sizes = [[0.057, 0.081], [0.141, 0.149], [0.173, 0.189], [0.202, 0.224]]
ratios = [[0.39, 0.83], [1.08, 1.48], [1.83, 2], [2.32, 2]]

Anyone can help me? Thanks a lot!