OK I see that your jet is actually back away from the throttle body already pretty far.
Brad has suggested before that one of these can help keep a uniform water mixture better than you might think:
http://store.yahoo.com/rodi/torfuelsav1.html
Sorry it was tornado not cyclone.
With a throttle body at one end of a long plenum you definitely want the water to be very well atomized and a uniform mixture by the throttle body or you will get rich and lean cylinders.
Previous experience has been with 4 cylinders and this setup - so water would still make it back to the last one on the line. Maybe getting past all those intake pulses on a 6 cylinder presents added difficulty in a dry intake. However properly atomized it should still make it to all cylinders, theorectically.