The layout of the design, by its very nature, is one that will trap bubbles -- You are taking sections of glass and capping them, which has a great potential for trapping air under the cap (especially if the sections of glass are not really tight fitting).
A few things to consider trying:
* Add a bubble squeeze. Here's my usual squeeze: Ramp appropriately to 1100 deg F, hold 30 minutes, and then ramp 50 deg/hr from 1100 to 1250, hold 60 minutes. Continue as usual after the long hold.
* Fire on fiber paper, rather than a kiln shelf. Air is more likely to escape from under the piece with porous fiber paper as a base. Given the linearity of the location of the bubbles, I wonder if there is a slight depression in the shelf? (if so, the fiber paper would help)
* Reverse the layout prior to firing -- clear on the bottom and top with the pieces. Flip & re-fire if you really want the clear on top with the crisper lines.
Huh... wait, now that I read again, you DID put the clear on the bottom and pieces on top. Ignore #3, but that might be useful info for someone else
Another thought... 1490 deg F is pretty darned hot for a full fuse. If your kiln fires hot, then any small bubbles that would normally "add character" at a lower temperature could become a big problem. I would try reducing the heat 25-30 deg F.
Best, Dana W.