It's probably worth mentioning that I have heard some seller's have successfully defended INR disputes with the same tracking number over multiple (separate) orders. I don't know if this is because PayPal didn't notice the tracking numbers were identical or not, but I also think there is a slight difference  between qualifying for seller protection and a buyer's claim being unsuccessful, in that if a claim is unsuccessful, the original payment is retained by the seller and the buyer doesn't get a refund, whereas if seller protection comes into play, the payment is retained by the seller and the buyer is still refunded (so it's PayPal who loses out, and therefore they are presumably more stringent with their policies). 

In other words, while combining items does compromise protection, there's still a chance, even if small, you can defend an INR, but probably no chance you can defend a chargeback.