not that hard to understand, Quad -
each month, the monthly cups BEGIN in ALL games. Obviously these monthly cup sections are small (4 or 5 players), and finish relatively quickly. That is why, over the course of a month, there will be many monthly cup sections; new ones begin as soon as the previous section is filled.
Anyhow, these are all 'round one' sections. The winners of round one sections will automatically advance into round two sections. Depending on how many entries there were to begin, there might be 5 entries playing ONE round two section, or perhaps 9 entries placed in two round 2 sections, etc. Considering that it is usually DIFFICULT to advance to round two sections, there won't be that many. And - if there are several round 2 sections, then the winners of THESE (now we are probably down to around 2 or 3 players) will advance to a round 3 section, to determine the winner of the monthly cup. (No May monthly cup sections will begin in June; no June monthly cup sections will begin in July, etc.) So we can always expect a relatively small number of sections in these monthly cups.
For certain games, all sections of a monthly cup might finish pretty quickly (maybe, for example, FIR); for certain games, the sections of a monthly cup will finish real slowly, and might extend OVER A YEAR, for example, Chess. But that's the monthly cups.
The advantage of monthly cups is that ANYBODY CAN ENTER, and therefor it allows beginning players the opportunity to play against extremely advanced players; sometimes even the 'champ'. A disadvantage of monthly cups (at least as I see it) is that advanced players will sometimes POUNCE on a section filled with beginners, with the expectation of wiping everybody out really easily. It is their 'free pass' into the second round. While I am personally not pleased with this arrangement, I can understand it and admit that the advantages may balance the drawbacks. I say 'may'.
Technically, if a player wishes to play in a rated tournament against players of similar strength to their own, they belong in the 'championship', where the computer will place them in the appropriate section. If you are like me - with not enough time to compete in championship sections - then this is not quite the ideal solution. I will say that the 'infinity' tournaments are a step in the right direction, in my humble opinion. Hope this helps.
(meow)