[justDankin]

Using the TTL, we figured out that the censor kicks in at the kth hop. This kth box belonged to Airtel.

If a box was censoring after Airtel, we would have received a clean response (ICMP timeout) at hop k as well. Of course, the TTL itself can change during the run, but that wouldn't happen for so many cases :)

[iso1631]

If you used an allowed domain name, did you get TTL expired messages back when using TTL=5/6/7/8?

[justDankin]

Yes, that was the case