Selection strategy of hyperparameter: pos_num?

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Hi, I have some questions about the hyper parameter: pos_num. In paper, you said "2)The projection of this ground-truth object’s center point locate within this feature map bin." But in practice, a torch.topk() function is used to get the positive target location, which is assigned by pos_num=1. And all the configs' pos_num are set to 1. Here comes my questions:
1)Is this configuration similar with that written in your paper?
2)Why only one point is assigned?
3)Did you do ablation experiments about the selection of it?
Thanks for answering!