I have four computers running BOINC in my workplace. In two of

those the percentage of time the BOINC client is running is ~ 5 %
whereas for the other two the figure is ~ 70 % even though I have set
the same preference ( run always ) on all four and they run for the
same
duration ( ~ 8 hrs.) on weekdays.
Could you please explain why this is so and if there is a way to
improve upon this figure ?

Atanu, welcome aboard.

I would first find out if it is a cosmetic bug (i.e. their are all running the same time but percentage is wrongly reported) or if the other two are mostly sitting idle hence percentage is correct.

Do you have do work while computer in use and preemtive set to on?

Also, I can see 5 machines under your account; two of them are on Windows 98.
I remember that CPU timers on Win 9x is a nightmare (see SETI Beta for example).

Which 'all' running at the same time? He's talking about the amount of time BOINC client is running, which is used to calculate if host will meet a deadline, not about workunit progress percentage.