Column modifiers (3rd edition)

[stodge]

For direct fire, some fire values are:

7 11 16 22 30 45+

If my fire value is 21 I roll on the 16 column.
A -1 column modifier changes that to a roll on the 11 column?

Is this correct? The reason I ask is that the column modifiers are brutal for the attacker using direct fire as it seriously reduces their fire power. No wonder my battlefield is littered with demoralised and disrupted units and not many bodies!

Thanks