How to change anchor size?

Since the sizes of my input images are smaller than the original COCO or PASCAL pictures, I want to change the anchor size accordingly to make my model better. Then my objects to be detected are of a nearly fixed size and the ratio between width and height is almost fixed. So I want to change the ratios and scales too. But after I change it, for example, change sizes=[16, 32, 64, 128, 256], strides=[4, 8, 16, 32, 64] to sizes=[32, 64, 128, 256, 512], strides=[8, 16, 32, 64, 128], the detections are scaled down to localized in a corner, so I think I have make a mistake. So could anyone give me some help to tell me, How can I modify this parameters to change the anchor size. Thank you.

[Kongsea]

Thank you for your quick answer and kind advice. I will have a try and investigate it.

[Kongsea]

OK, I will close it now. Thank you.