Hello, Wolfgang.
Try use follow code:
but I don't sure that is help to you, because your question related to specific scanner (ie that question don't related with a Saraff.Twain.NET). I advice send this question to a Epson Support Service.
Try use follow code:
if(_twain32.Capabilities.OverScan.IsSupported(TwQC.Set)) {
_twain32.Capabilities.OverScan.Set(TwOV.All);
}