Three possible bugs

[Stirling]

Tested a little:

An M1A2 started with 4 shots and used them all zfiring 1 hex. Over 1 hex it used just one. It could zfire through 6 hexes of trees

An M2A2 started with 6 shots and used 2 each adjacent zfire. Over 1 hex it used just one. It could zfire through 5 hexes of trees.

I rarely use zfire, so I can't say if this is normal or not.

[narwan]

My Z-fire was all with infantry type units, those used up 4 shots for 1 round of 1-hex area fire.

Are you sure there was no elevation difference restricting the 'LOS' through to the woods to those distances? Note that some 'normal' elevation terrain can go up as high as 4 feet which won't show as an actual elevation level increase but will restrict LOS.

Narwan

[Stirling]

In adjacent zfire it appears that each weapon slot uses a shot. Non-adjacent usually uses one shot total.

Hex ranges weren't entirely consistent due to elevation differences, as you point out. Infantry could zfire 4-6 hexes in my test. Vehicles varied from 5-8.

Like I say, I don't know what normal behavior is.

[Pyros]

I confirm what Narwan mentioned, but I am not sure if this is connected with the range of attack.
I have experienced something similar when Z-firing from a Gunship.

cheers,
Pyros