Likewise we are at 85% and this number remains within 1% no matter what shipping method we use. That being said we have switched to RM 24/48 tracked to see if that will make any difference, so far no change.
FYI - On a recent (and rare ) chat with Amazon on a different matter we were "verbally" warned that if we didn't get out VTR to <95% within 1 month we would be suspended. With this warning we sent the tracking details showing our current rate was actually 97% that had tracking numbers but about 11% were showing as undelivered. Amz response was for us to use a better carrier with a fully tracked service! - we are waiting to see what will happen in 2 weeks time when the 30 days is up!
I wondered how those of you with a Buy Shipping integrating are doing regarding your VTR scores. Does having the integration via Linnworks make a difference or have you seen a rapid decrease in your score anyway? We are at 85% but I'm holding off using Buy Shipping as I'm not sure it is working as they would wish.