Wagering games with variable reel sizes and gaming devices for playing the same

Gaming devices, gaming systems, methods of conducting a wagering game, and computer programs for initiating a wagering game are presented herein. A gaming device is presented that includes a wager input device, a display, and a wagering game. The wagering game includes a plurality of reels each having distinct symbol positions and bearing an array of symbols. Some of the symbols are grouped into corresponding symbol clumps. A window is associated with each of the reels. The display displays outcomes of the wagering game. Some of the outcomes are represented by a segment of each reel being displayed through a respective one of the windows. The probability that a particular one of the windows will be filled with one of the symbol clumps as part of an outcome decreases between at least two of the windows.