Last night I achieved what you just attempted in 2013, in Ultra Moon in the "Ultra space wilds" my method was just throwing Premier Poke-balls at it 1x rate you could try poke-balls as they are cheaper to obtain. The reason I went with a Premier ball instead of a regular pokeball was because, Shiny Palkia would look good still in a Premier poke-ball. So I had 4 Love balls in stock, So I said why not throw the love ball at it, as it almost got caught the last time. As you imagined it worked: theory is luck, but also judging how close you are at catching it with another pokeball. You can almost sense you are getting closer. And take a chance, but make sure you have extra balls for what you have planed.