How to make this file to mockup and keep the shadow

I tried use attached photo to make a mock up PSD

1. Add a layer and converted to smart object
2. Place image into smart object layer and adjust to fit the frame
3. Duplicated photo as third layer (shadow layer) and put it before the smart object layer
4. Select the blank area in frame
5. Select color rage → shadow → adjust to almost same as shadow
6. Add mask to shadow layer
7. Blend shadow layer to multiply
8. Make shadow layer to opacity to around 25

How ever, the shadow still looks not natural, any steps I missed or any good suggestions ?