Will filler directly under by bottom lip create a more natural, rounded effect? (photo)

Hi and thank you for sharing your question and picture! We can use hyaluronic acid fillers to add volume to the lips, as well as creating better defined lips. It would be best to see some pictures from prior to your lip injections, to see if the dip you are mentioning is created or exacerbated by the filler injection. In that case, partial removal of the filler with hyaluronidase followed by some additional revisions can help. It is very important to work with a physician with great skills and experience in lip injections. I hope it helps and good luck! 

The changes you are looking for demand a great deal of expertise to accomplish well because the lips are finely structured and easily overfilled. I would recommend a hyaluronic-acid based filler such as Restylane Silk or Belotero. Consulting with a board-certified dermatologist who can show you beautiful results in similar cases will give you the best and most natural-looking outcome.

Yes, what you are describing can be achieved.  You are correct that filling closer to the "dip" of the lip in a certain way would create a more rounded lower lip that correctly matches the top lip.  Please see a Board Certified Plastic Surgeon with experience in lip injections.  I hope this was helpful to you.  
Best Wishes, Dr. B.
Plastic Surgery Plus

 Hi, I have performed many lip augmentation procedures using dermal fillers or lip implants for over 30 years.  You could try one of the thinner lip fillers like Juvederm or Restylane to see if its gets the result you're looking for.  Since part of this vermillion border is thicker skin below the lower lip, it may prove challenging to create a localized curvature in that specific area. Following my beauty principles, the upper lip should be approximately 75 % the size of the lower lip for the lips to appear balanced. The lips can be augmented using a dermal filler or a Permalip implant.
 Dermal filers and lip implants offer a much more reliable volume for augmentation of the lips than permanent fillers or fat injections which are associated with increased, unwanted, side effects.
Hope this helps