diff --git a/openems.cpp b/openems.cpp
index 8489257..c34c17a 100644
--- a/openems.cpp
+++ b/openems.cpp
@@ -734,12 +734,13 @@ int openEMS::SetupFDTD(const char* file)
 		{
 			for (int p=0;p<3;++p)
 				pos[p] = FDTD_Op->GetNumberOfLines(p)/2;
-			pos[n] = 10;
+
+			pos[n] *= 1/4;
 			Op_Ext_SSD->Add_E_Probe(pos, 0);
 			Op_Ext_SSD->Add_E_Probe(pos, 1);
 			Op_Ext_SSD->Add_E_Probe(pos, 2);
 
-			pos[n] = FDTD_Op->GetNumberOfLines(n)-10;
+			pos[n] *= 3/4;
 			Op_Ext_SSD->Add_E_Probe(pos, 0);
 			Op_Ext_SSD->Add_E_Probe(pos, 1);
 			Op_Ext_SSD->Add_E_Probe(pos, 2);