The provided doll has a usual polyfoam core and the silicone does not adhere at all. Therefore, “adding/injecting” more silica in this area will not solve the problem, which will make the situation worse. It may be that the foam core "floats/moves" in the mold and the silicone is poured, causing the skin to thin in these areas... you can't do much! There is no "mechanical/glue" to adhere the silicone to the foam... this is the problem of placing the foam core precisely in the center of the mold. This will allow the correct amount of silicone to wrap around the foam, not much I can add. Sorry, but it sounds like you have a defective sex doll in the factory.
The Difference Between Real Sex Doll's EVO Skeleton And Ordinary Skeleton
2020 New Year Sex Doll Promotion
Description of Delivery Time For Urdolls Sex Dolls