Slitherine

LF LF LF
LF LF LF

CV CV
CV CV
Here we have six lf facing south, the cv are facing north and pinning the lf to their front.
The lf turn east and form a column and move of leaving part of their last base just in front of cv.
Q have they reduced their frontage as they are now the same width to the cv as they were before they turned and moved?

Providing the LF end further away it doesn't matter.

If they do not end further away they cannot do this.

They can only: advance directly forward; wheel towards; remain in place (turn if they want); Move to end further away

Yes, as Phil said. If you are wondering about the turn being a contraction since you went from 3 wide to 2 wide, that isn't what the authors care about. They don't want you to be able to stay in place and contract frontage. The reasoning is that the enemy might have a unit in position for a flank charge and the contraction would take the contracting unit out of the range of the flank charge without actually moving away. Sorry I can't remember which post that was from.

Their semi-official answer on RAs is:
viewtopic.php?f=43&t=10008

From memory turning 90 degrees on the spot without any further movement is also an option. But I agree with Phil that the OP is illegal.

From memory turning 90 degrees on the spot without any further movement is also an option.

Yes, that is what the book says. I hope my post didn't confuse. You can turn on the spot and have a smaller frontage due to the turn mechanism but you can't stay facing the same way and contract frontage.