You are absolutely right, the set minimum of the polar axis is disregarded and it is internally forced to a zero. This is because leaving the polar axis with a minimum different than a zero might lead to an unclear visual representation. However, I will ask that you provide us with some snapshots(drawings of some sort) that depict the output you need, so that we can consider changing this.
Currently we do not have any implemented work arounds for this. If this is a must in your application, we may be able to suggest something, but keep in mind that it will most likely be some heavy work, as this is not a built-in feature an you will have to fight the internal logic of the control.
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