Of all the places we do fat grafting, the area with the narrowest margin for error and with greatest complications, is the lower eyelid....at least in my opinion. I would make sure that filler has completely resorbed or been dissolved before proceeding with fat grafting to the lower lids. If you feel the area below your eyelid (the lid cheek junction), you can tell immediately that there is very little space between the skin and the bone. Because of that, there is not much room to place the fat and a high likelihood that it will look lumpy. I would suggest that you see an experienced surgeon because I believe it is necessary to use very small amounts of fat in that location.