infill modifier mesh gets printed first

[surfski 0]

I print my parts "lying down" due to strength requirements.  This places the top and bottom on the "left" and "right" (actual location varies due to part placement).  So, I use modifiers to achieve the additional solid thickness required at the real-world top and bottom (thicker than the walls).   However, Cura wants to print one of the modifiers (the part's real world bottom), an interior infill section, before the part's walls.  This causes some defects.  I'd like it to print the walls first, as usual, and then the modified infill sections as part of the infill, just with higher density than the rest of the part.  It does print the top modified infill as desired, after the walls.  Part of the difference may be due to the user specified Z seam alignment, as the bottom is located at the desired Z seam location, while the top is at the opposite end of the build plate.  To be clear, the current modifiers are the entire top and bottom 5mm of the part.  I haven't tried modifiers that are just the interior (minus the wall thickness), which I could do, but it's more of a modeling hassle.

 

For the modified sections, I use either increased Wall Line Count, or 100% Infill Density, although Wall Line Count seems better or at least faster, even though it's really 100% infill that I'm after.

 

Speaking of the Z seam, I'd like it to be at the "center of the bottom" of the part - a flat section, not a corner.  The only way I've been able to achieve this is to add a "fake" corner at that location via an extruded polygon (which I then grind off after printing).  Is there any other way to force the Z seam to be at a location that's not a corner?  

 

Screen shot shows the bottom printed, and the outer wall starting off.