Emulsions may not necessarily be thinner. An AgBrI may have core I, distributed I or surface I. Each of these will develop differently all other things being equal such as thickness and grain size. Addenda, gelatin type and other factors influence development rate as well. This is why a divided developer is so chancy. It must be fine tuned for the emulsion thickness, gelatin type and emulsion type. It is not necessarily a good idea to rely on divided developers, stand development or other techniques such as this across films. Each of these must be fine tuned for each film and process condition before it will work best.