Need some help in solutioning area, kind of how to size and scale a websphere environment. Inputs like hardware type, number of concurrent users, complexity of the application hosted.

Explored this link: 
www-304.ibm.com/partnerworld/wps/sizing/...

But unfortunately this only cater to specific type, no documentation about the logic of sizing or general understandng of it.

Any document link reagrding the same will be much appreciated. Thanks.