Do not make comparisons against the EU Nacra 20's. Their sails are quite different and thus the tuning is quite different. Yes, I speak from experience. No, you can't touch this.

Halfway down the transom is the way to go with E/P sails, unless it's a complete drifter. Bring it forward a pin or so then. Spreader rake, well, 1.75 inches sounds good to me. 600 diamond tension is pretty frickin' low. I'd stay in the 675-800 ranges, always.

PS: Tad's spinnaker looks like Ronald McDonald's underpants.