Question about Train Config Generation App.

I want to get the anchor setting of my dataset, the example you showed is as follows:
pyodi train-config generation \\
$TINY_COCO_ANIMAL/annotations/train.json \\
--input-size [1280,720] \\
--n-ratios 3 --n-scales 3

 However, for Faster R-CNN, the size of input image is not fixed, in this case, how should I set the ' --input-size'?