I just got unbanned after a two week ban, I have a question about ban duration.

I originally got an insta-permaban for some questionable things I said in chat, but after talking to support I got it reduced to a two week ban. I'm wondering how long it would take for the ban duration (for the next ban) to decrease? From now on I'm either going to play League with my friends or if not, say something only if its helpful to winning the game, but I just feel uncomfortable knowing that my next ban would be a permaban and I'm just curious if the ban duration will ever decrease. Thanks!