I want to say the sentence "In the 1930s production focused on/ on the smaller cars"
So, I think that is: In den 1930er Jahren fokussierte die Produktion auf kleinere Autos.
The only reason I used 'auf kleiner Autos' is because I googled the phrase and saw it used in a headline! I don't actually know why it's 'kleinerE' though. My first sentence said "In den 1930er Jahren fokussierte die Produktion auf den kleineren Autos" because I assumed (going by the adjective ending tables) that 'auf den kleineren' would be correct. I'm really confused now as to which it is. Are both correct? Or both wrong?! If 'kleinere' is correct, why is the ending 'e' when 'auf' is in front of it?
Hope someone can help, I'm awful with adjective endings.