Changed nozzle sizes on my Taz 6, cannot seem to dial in my settings...

I swapped from a 0.5mm to 0.4mm nozzle on my Taz 6, and I cannot seem to get my settings dialed in properly in Simplify3D. Lines appear waaay too far apart no matter what I do. Here’s what it looks like: http://imgur.com/a/5TvC4
First I (duh) changed the nozzle diameter setting. I adjusted the Z-offset in S3D so the first layer at 90% height is squished nicely. From there I’ve been playing with extrusion multiplier, extrusion width (I’ve tried between 0.4-0.48), first layer width, first layer height, etc. No matter what I do the lines appear way too far apart and the line width almost seems inconsistent. If I move the nozzle reaaaally close to the bed and up the extrusion multiplier it squishes it all nicely and the gaps disappear, but then subsequent layers are very messy.Any ideas? Are there any settings other than nozzle diameter and extrusion width that need to be tweaked after changing nozzle sizes?