Thanks for contacting us! There is a workaround to achieve a wider than 100% inner border:
1. Apply Museum Matte with the outer border at 0% and inner border at 100%.
2. Apply Museum Matte again, and adjust the inner/outer borders as desired.
3. Go to the Effects tab > Doodle tool (towards the end of the page).
4. Click the Color selector, and then click on the inner border (to ‘Pick’ this color)
5. Paint over the unwanted drop-shadow between the 2 inner borders that were applied.
Let us know if you have any further questions.