Hey Erica,
I agree that the algorithm that sourced the images for portfolio items was unnecessarily complicated; thank you for bringing this up! I’ve completely re-thought it and here’s what I came up with. Please upload the contained file into the theme folder and let me know if it does what you needed (which is, showing the thumbnail as the portfolio item background and the content image as the on-click overlay).
Sincerely,
Andrii / Satori Studio