I am clustering customers using their stay time on our web sites. When I only use one variable, time, for K-Means clustering with 10 clusters, customers look unevenly distributed to each clusters.
However, when I used 5 variables, time with 4 different categorical variables, K-Means clustering tends to cluster even number of customers to each cluster. I'd like to know why this happens and which clustering results are good or bad between evenly or unevenly distributed data and why clusteres tend to cluster evenly distributed when I added more variables. Here I mean "(un)evenly" as the "(un)even" number of points assigned to each cluster.
Here is the picture of clustering result with time variable only. My applogies to the low quality of drawing.
Here is another picutre of clustering result with 3 principal components from 5 different variables(time and 4 different categorical variables).

