Trouble wiring a double row of droppers

The problem seems simple enough. I want to power a double row of droppers. My idea was to redstone wire it this way:

Take a double decker row of droppers, and run redstone across the top. However, repeatedly poking the button, only fires 13 of the 16 droppers. The three bottom droppers next to the yellow wool do not fire.

Any idea why this might be? There is no redstone within several blocks of the droppers. Sometimes I wire this up, in slightly different contexts, and get all 16 to fire, sometimes just 15 .... Is there a simple explanation as to why this wiring scheme will not work? I'd hoped to do this, so I could put a hopper filling system on the back end, filling all these droppers, so I wanted to avoid wiring them from the back, and wanted to just do the top...

Edit: Here's the proposed hopper filling system. This will be connected to a massive farm, so this is in fact "efficient" for my needs.