Firing through Light Woods into Light Woods

[saracv3]

Given the diagram under 8.3 4th ed., Unit B fires at Unit C. This attack passes through one light woods hex into another light woods hex.. Is this attack a  -1 modifier or a -2 modifier (each light woods hex = -1)? RaW specify passing through light woods is -1, but target could be in clear hex, etc.;  I believe I play a -1 modifier for attack.

House Rule possibility here?

[Hugmenot]

We've always played it as -1 total, not -1 per hex.