It is good to buy the dip of the coins who are reliable .Buying the Dip of startup altcoins that is under development which has not gained stand yet is not advisable enough. As for me , i calculate a lot when i want to buy the dip . I always ensure i buy only altcoins that is not above 25th rank in coinmarketcap.com and this has been working well for me.
The method you did was right and it might be imitated, this method is also widely used by investors by looking at the coin's ranking on coinmarketcap, it might be safer if it was reduced to the top 10 rankings, because when there is a decline, the possibility to restore its value is still there.