No, I kind of came to the same conclusion you did with the 2 to 7%. When I was buying Eth, both Eth and BTC were up, but they are both down. If I waited until Eth was up, it would be more than likely that BTC would also be up since BTC moves first, so at this point, it probably doesnt matter too much to make a huge difference. With Linear thinking, Eth would be back up to $4500-$5000 and BTC would stay the same. lol, not happening.
Can you tell us how much was your budget for buying ETH back then and what was the price of bitcoin when you did?
This will probably help us to find a better solution instead of just suggesting you hold on until a new ATH appears. But maybe, if you have extra budget then it's better to accumulate as much as you can afford. ETH will follow the bitcoin trend, but if you have any doubts then invest in bitcoin instead.