SSD anchors in Tensorflow detection API

System information

• What is the top-level directory of the model you are using:
  models/research/object_detection/ssd_mobilenet_v2_coco
• Have I written custom code (as opposed to using a stock example script provided in TensorFlow): No
• OS Platform and Distribution (e.g., Linux Ubuntu 16.04): Ubuntu 16.04
• Mobile device (e.g. iPhone 8, Pixel 2, Samsung Galaxy) if the issue happens on mobile device: Non
• TensorFlow installed from (source or binary): binary
• TensorFlow version (use command below): 1.12
• Python version: python2.7
• CUDA/cuDNN version: CUDA 10.0/ cuDNN 7.4.1
• GPU model and memory: 1080Ti, 12GB

Describe the problem
Default SSD_mobilenet_V2_config is below.

anchor_generator {
  ssd_anchor_generator {
    num_layers: 6
    min_scale: 0.2
    max_scale: 0.9
    aspect_ratios: 1.0
    aspect_ratios: 2.0
    aspect_ratios: 0.5
    aspect_ratios: 3.0
    aspect_ratios: 0.33
    }
}
image_resizer {
      fixed_shape_resizer {
        height: 300
        width: 300
      }
}

If I set image_resizer {width:600, height:450} (4:3 input size), would base_anchor_size be set square or rectangle? link

image_resizer {
      fixed_shape_resizer {
        height: 450
        width: 600
      }
}

I trace the ssd_anchor_create func code, it seems to set rectangle-like base_anchor_size, right?

    min_im_shape = tf.minimum(im_height, im_width)
    scale_height = min_im_shape / im_height
    scale_width = min_im_shape / im_width
    base_anchor_size = [
        scale_height * self._base_anchor_size[0],
        scale_width * self._base_anchor_size[1]
    ]

I want to ask how could I set specific size of anchor box for each layer?
How to check details of anchor bboxes after training model?
Thanks a lot