You are correct that a chin implant would normally not augment the area in blue that you are highlighting in your picture. This area is higher than the implant would normally go. In my opinion, if you wanted to augment that higher area after replacing your current implant with a larger one, I would recommend using a filler.
Hi, I have performed many Chin Augmentations using chin implants for over 30 years. From the photos, your chin is weak. A weak chin creates an imbalance making the nose appear larger, the mid face top heavy and the lower face look short that de-emphasizes the lips and allows early formation of a double chin. Chin augmentation using a chin implant will add projection to the chin creating harmony and balance to the lower face. I have found that placement of a silastic chin implant, through a small curved incision under the chin (also allows excess skin removal) to be very safe, quick, highly effective and far less invasive than a sliding genioplasty. I perform chin implant surgery in 30 minutes or less, often using a local anesthetic alone. In my opinion, you are a good candidate for chin implant surgery.
Hope this helps.