Thread drift.

Jeez, I wish I had caught this before I did my Di2 build. The Junction A rubber strap stopped me for a bit, you are correct that Shimano is less then helpful in that they should have stated “Trim the strap with scissors so that the strap is tight and secure with no excess to interfere with the junction mounting, also trim BOTH sides of the strap equally so that the Shimano name on the top of the stem on the strap is centered”. And of course I pondered the battery parts including the washers and ring clip, before finally testing if just the Ritchey mount wrapped around the battery and shoved up inside the post would hold. It does, nothing complicated about it.