Hi @philipp.rockenschaubDDSYJ. Only the folks at Autodesk, who wrote the source code for the Inventor software might possibly be able to explain that numbering system. Natural index numbers are generally assigned in the order that the objects they represent were originally created, or originally existed. In situations were it seems like multiple pieces of geometry will be (or have been) created at the same time, it can be very difficult to predict (or explain) why they are in that specific order. Did you know that you could assign a name to things like Vertex, Edge, & Face objects in a part document? Manually, you can simply select that edge, then right click, and choose 'Assign Name...' or 'Assign Entity Name' from the right click menu. Then when you fill in the name prompt and click OK, it will usually create a visible tag on that object, with the name you assigned it. And it will usually create a new sub tab within the iLogic tab named 'Entities', and it will include a reference in the list to that named geometry. Then you can find that named geometry in an iLogic rule using the iLogicVb.Automation.GetNamedGeometry method, and the associated tools under the object.
Dim oDoc As Document = ThisDoc.Document
oNEs = iLogicVb.Automation.GetNamedEntities(oDoc)
oMyNamedEntity = oNEs.TryGetEntity("Entity Name")
Wesley Crihfield

(Not an Autodesk Employee)