The 80 p free extra move must be "in either side's bound". If you do it half way through your move it is in your bound, so it is permissable.
If you insist on any oblique movement ending lined up in combat then I would do a zig-zag ending lined up in combat. This would be part of the normal move, not the 80 p extra.
Both of these are consistent with the "must move into close combat if they would in real life" principle.
IMO Phil meant oblique group moves to be permitted to enable the group to move into combat lined up, even if the actual contact was the result of a forward move segment. I note that there is no limit to the amount of oblique or sideways movement allowed to line up in combat, which opens up some unexpected possibilities.