The ISurfaceOp.Visibility() method ignores the OFFSETB value in ArcObjects SDK for the Microsoft .NET Framework 10.6.1 and newer releases.

Workaround

Set the AvolidDataConverstion property to true on the IRasterAnalysisGlobalEnvironment interface to allow the ArcObjects SDK 10.x Spatial Analyst execution path to be used. Insert the following 2 lines right before the Visibility method is called.

IRasterAnalysisGlobalEnvironment globalEnv = (IRasterAnalysisGlobalEnvironment)sop;

globalEnv.AvoidDataConversion = true;

Steps to Reproduce