However, if the agent doesn't provide a range, I'm not going to follow up at all. I'm going to just let it go.

I think that will keep me from going insane.
Please,
do not do this. If you hear nothing, assume they didn't get it rather than assuming they rejected you. Email gets sent to spam folders/eaten by the ether. Mail gets misplaced/lost/shredded. Overworked assistants miss stuff. Accidents happen all the time.
The agent I eventually signed with didn't respond to my first e-query. I followed up with a snail mail query two months later, which turned into a full request then an offer within two weeks. If I'd assumed "no repsonse means no", I wouldn't be signed with the kick-ass agent I have now.
Follow up on "no replies". Re-query -
it can't hurt. The worst thing that can happen is more white noise, or an actual rejection. The best that can happen is an offer. (Very cute puppy in your avatar btw

)
Congrats on the full Amy!