Battle Ping custom strings for WoW and cross-realm latency

Greetings,

I've been using Battleping for a few days due to current ISP routing failure and it does indeed provide a significant latency reduction, at least when i play on my own realm and i do not join cross realm parties/ raids.

Once i join any cross-realm party/ raid, latency shoots through the roof again.
I would like to know why this is the case.

To my understanding, my own ISP does not dynamically reroute my network packets depending on the content i'm doing or the players i'm playing with, regardless of their server.

Still, before the afore-mentioned ISP routing failures, my latency always remained pretty stable, almost identical to my own realm latency, regardless of what party/ raid/ cross-realm i was joining.

So what is happening exactly with the Battleping routing Vs ISP routing ?

I've also heard there were some codes which might alter this functionality, and i'd like to learn more about this.

Thank you.