Power Delivery Network (PDN) Tool

From the image, it does appear as if you have put the decoupling capacitors on round pads in a mirrored location to the BGA pads. The caps are not directly on the vias.

Here's a photo of the bottom of the PCB on one of the CARMA board FPGAs. Note how the decoupling caps are actually on top of the tented vias.

The square pads are slightly offset due to the fact that we initially tried not tenting the vias. However, too much solder wicked into the vias, so we had them tented (and didn't bother centering the cap pads in the vias).

Cheers,

Dave