django-storage[s3]: using storage and upload_to field together on image field doesnt work

Question

There are sevaral threads/blogs on how you can use django-storage library to upload files/images on different cloud platforms(in my case I'm concerned about only S3).

I followed those and configured it by adding below settings in settings.py

storages to INSTALLED_APPS,

AWS config

AWS_ACCESS_KEY_ID = 
AWS_SECRET_ACCESS_KEY = 
AWS_STORAGE_BUCKET_NAME = 
AWS_S3_REGION_NAME = 
AWS_QUERYSTRING_AUTH = False

STORAGES = {
    "default": {
        "BACKEND": "path.to.CustomStoragBackendsClass",
    },
    "staticfiles": {
        "BACKEND": "django.contrib.staticfiles.storage.StaticFilesStorage",
    },
}

class CustomStoragBackendsClass(S3Boto3Storage):
    default_acl = 'public-read'

Now in models, I'm trying to use this as below

class MyModel(mdoel.Model):
    ...
    main_icon = models.ImageField(
           null=True, 
           storage=CustomStoragBackendsClass(location="my_model/main_icons"),
           upload_to=main_icon_upload_to_path,
    )
    ...

and here is the upload_to path function in the same model file

def main_icon_upload_to_path(instance, filename):
    return f"{instance.pk}/{filename}"

At first look all this looks fine but for some reason it's not working as expected. I'm still getting the path without instance id in it (basically it seems upload_to is not being used at all, only storage field is being used).

My goal is to have a single bucket for all images/files in the app. and then in that bucket will have folders representing each models from where files have been uploaded. and with in model directory, I have another folder which represents the field name, and then id of that model object and so on. here are few examples to make it more clear.

path1 = S3Bucket_name/model1_name/model1_field1_name/instance_id/file_name.png

path2 = S3Bucket_name/model1_name/model1_field2_name/instance_id/file_name.pdf

path3 = S3Bucket_name/model2_name/model2_field1_name/instance_id/file_name.jpg

tried by providing the full path in upload_to field itself, but that didn't work either. not sure if i'm missing anything.