Bicycle Mechanics - Handlebar Science ?

--- Has anyone published a study on the efficacy of various positions of the handlebar grips in relation to the stempost? In some bikes the grips are well -behind- the stem, in others the handgrips are ahead of the stem. Seems to me the best leverage and control is to have the stempost in a straight line -between- the handgrips.
Any opinions based upon experience?

I assume by "stempost" you mean the fork's steerer tube.

Leverage and (steering) efficiency aren't the controlling factors in bicycle handling. You don't need much strength to turn a bicycle and the actual amount the handlebars are turned (except for U-turns in a narrow street) is very small. This is true even for MTBs.

The position of the handlebars and ,as a result the rider's hands, is important two major considerations.

1. How upright a position they allow. Having the grips rearward allow the rider to sit very upright and is ok for short trips and very casual riders. Having them further forward puts more weight on the hands and allows a much more aerodynamic position. Within reason it also allows the rider to generate more force and power. Both the aerodynamic and power advantages are very important to fast and long distance riders. The ultimate application of this principle are the aerobars used in time trials and triathlons that put the riders hands very far ahead of the steerer.

2. Hand position controls weight distribution. This has an influence on bicycle stability and cornering control at faster speeds and is very important for controlling the bike on steep assents and descents as MTB riders often do.