These types of light tents do a very good job for small items but they are a pain to set up and take down unless you have a dedicated area where you can leave it up. I have tried a white sheet as you have and later tried a white piece of remnant fabric which was thinner than the sheet from Wal-Mart.
I purchased this Folding Light BoX
a few years ago. Eh? It was $50.00 when I purchased mine.
Here's one of my many bowls from the light box.
I can't tell but it looks like one of your bulbs is a different color temperature. There's a slight yellow cast from the left light. Are you using 5500k CFL's?