Nice explanation of second scoping!
My own tips for sniper vs sniper are probably the following:
1) Know the sight lines of the map you're playing so you can tackle a given situation from a different perspective,
2) increase your firing speed so that even if you're missing more shots, you'll be hitting the ones you do hit at a faster rate, improving your dps output (which tbh, is the whole purpose of the sniper class),
3) always be moving, even when taking your shots, as if you're playing stepmania,
and most important, 4) don't ever feel bad if someone else is a better counter-sniper than you, there are so many variables that go into a game, and despite being terrible at counter-sniping I still played sniper for a ugc plat team due to my other strengths :^)
Otherwise, sniper is one of the few classes that you can only really get better with through practice and time commitment.