Well said. I happen to concur with you, good observation that Nadal has a tendency to go far behind the baseline when he does not feel comfortable during the match. The only exception would be clay, where he seems to always play far behind the baseline nowadays and still can display a good level. Maybe next year Rafa will get used to return within the baseline even on clay? After Wimbledon 2019, I think Carlos Moyá and his technical stuff are encouraging Rafa to return within the baseline. It will be interesting to see if Rafa adopts this methodological tactic even on clay.
Correct me if I am wrong, but as far I am concerned Novak is more regular in his return tactical pattern. Novak returns within the baseline in every match, regardless of the court particularities. Regularity in the return execution is a sign of secutirity, which is unsurprising given the fact that Nole is widely considered, and rightfully so, to be the greatest returner of tennis.