Checkerboard:

At a recent dance, the caller called:
From a two-faced line, Checker board, crossfire

After the original trailers did their extend and crossfire, the caller wanted 
each mini-wave to slide into the vacated two spots in the "outside" line.

I certainly understood this analysis, but my original thought would be that each tandem would 
press 1/2 out to form C1 phantoms (those who did the crossfire in phantom columns and those 
who did the trade in phantom lines).

From two-faced lines Checkerboard, Lockit
Which would certainly (I think) end in C1 phantoms (as above)

* * * *

The "gestalt" for me, has always been that the "slide into the vacant spot" 
should NOT require any dancer to "cross" from one side to the other side 
in the "horizontal plane" (i.e. the parallel to where the two who traded worked). 
If, after an original trailer did the call, if they end on the CENTER line 
(perpendicular) to those who traded) then they could go forward or backwards 
to fill a spot, but I am not used to sliding from "one quadrant to another" as was 
expected by this "Checkerboard crossfire"

Is it really true that IF you can get back to a 2x4, that always "predominates" how to adjust back?

Are cases where you cannot get to a 2x4 now considered "improper"? 
If not, is there a general rule on how to adjust them?