text: Title: About anchor size
  Body: > Please correct me if I'm wrong for the following observations:
  > 
  > Based on @zyc-ai 's description, and the paper, anchors should be generated based on the size of template bounding box, but in the code, wherever Anchors is generated it was always through code like this:
  >         self.anchors = Anchors(cfg.ANCHOR.STRIDE,
  >                                cfg.ANCHOR.RATIOS,
  >                                cfg.ANCHOR.SCALES)
  > which will give anchors with constant size (64x64, before applying ratios). For generating positive classified anchors, one anchor box need to have >0.6 IOU with the ground truth, that means if the ground truth bounding box is much bigger or smaller than 64x64, no anchor will be considered positive during training, and that object won't be detected during tracking at all.
  > 
  > A workaround is to defined multiple anchor scales, but the paper claims only one scale is needed, which is very confusing. This will only happen if all the tracking objects are around the same 64x64 size in the search image.
  > 
  > Am I missing something? Please point out if there is code somewhere I've missed, thanks~!
  
  _Originally posted by @qinc in https://github.com/STVIR/pysot/issues/129#issuecomment-590620000_
  
  I have the same question about the anchor size setting. According to the code, anchor size is fixed to be 64x64( before applying ratios), which seems may cause the IoU < 0.6 for all anchors when the tracking target is extremely small. Can someone kindly point out if there are codes to change the anchor size according to the reference target box or why the constant anchor size works for the extremely small target cases.