Did you really use the REST API or https://community.jivesoftware.com/people/gauravg/avatar which is not the REST API - width and height are ignored here.
The URL must contain an ID and not the user name: https://community.jivesoftware.com/api/core/v3/people/147630/avatar - so you get a 128px² image. If the avatar was set manually then the size is usually 46px² or 48px².
You may want to fetch the profile images instead of the avatars if you need larger images.
Yes it makes sense. Thanks for the detail.