I'm not sure I see the difference between renkonti and renkontigxi. Transitive vs intransitive?
I think they are like Spanish "encontrarse con" and "quedar con". "Renkonti" means to find someone accidentally anywhere (you are walking on the streets and suddenly meet a friend) while "renkontigxi" means to meet someone on purpose in a determined time and place (you meet a friend in a café at 4 pm).
That's what I think. But I'm not completely sure.