The amount is now $9.5m, compared to $17.1m.
Horizon said the settlement will not affect the merger consideration to be received by stockholders.
A special meeting has been scheduled for 25 February, when holders will vote on the Matson takeover.
Matson plans to buy Horizon in a $450m deal which is to go forward after Horizon sells its Hawaii business and four ships to Pasha Hawaii.
As