Not sure on time frames between but you've made a marked improvement. Chests are funny things, I train a guy with genes like yours (naturally lean and muscular) he has trouble with his chest. He was doing some real weird exercises that he had picked up from the broscientist at the gym had taught him.
I switched everything up for him and hes starting to add size. Basics like heavy flat barbell, incline, incline db press, cable cross and db pullovers. Once you have basics heavy and see changes then switch it up and try new things.
Hope the brotips helped brah