Slitherine

Hi
A question on supporting movement. The scenario follows:
2 BG(of 4 bases) are fighting with a base offset:

....XX
....XX
..yy
..yy


........zz
........zz

Thus BG, "X" and BG "y" are fighting with the maximum of 4 die per BG.
No elements can be fed into battle, because all the bases are fighting.
Now, BG "z" wants to join the combat, but for various reasons (failed test/player forgot to charge)
did not charge. In the movement phase, can BG "z" join the battle as an overlap, or the frontal fight?
I can think of three possible solutions (after the movement phase):
a:
...XX
...XX
..yyzz
..yyzz
("z" moves into frontal contact and fight in the mellee phase)

b:
..XX
..XX
.yy.zz
.yy.zz
("z" moves into overlap position and fights in the melle phase)

c:
"z" waits until the next turn and try to charge again.

We payed the c: option, but it seems strange that because the original fighting formation is a mutial overlap, that a
third battle group can not join it in the movement phase, where if the groups were lined up the third BG can join in an overlap position.
Thanks

You played it correctly. Any other way would be a way of getting into head on combat and avoiding the impact phase.