I only needed one more item to “unlock extra savings up to 15%”, so I added an extra item to see what the savings would be. I didn’t think the savings matched what was advertised, so I removed an item to see what the difference was (making sure to screenshot before/after this time). Turns out the price of 3 out of 4 items is the same after an extra 5% discount.
I do the same. Using VPN, proxy, Firefox container, tracker blocking, the whole 9 yards. I haven’t seen price change based on location/purchase history. I’ve been looking for signs of this for a while. Prices do fluctuate quite a bit though. The site might have auto-selected a different “ships from” option for you, depending on how you’re logged in.