I can explain, the League Champions of Europes top nations automatically go into pot 1, the teams in pots 2, 3 and 4 are in order of coefficient (ranking based on the past 5 season in both European competitions) so, you basically have the top 16 teams over the past 5 seasons in Europe split into pot 1 and 2. Unless there's a surprise Like Leics or maybe Monaco winning the League. League Champions going into Pot 1. (Leics were in pot1 last season). So you have Juve (Champions) with Barca (runners up remember), Madrid (champions ) with Dortmund (high coefficient) Munich (champions) with PSG (runners up remember) and so on. Leipzig finished runners up in Germany, but haven't played in Europe in the 5 year period, so their coefficient was low, hence them being in Pot 4.