us managers can be damn bad sometimes
been having a think today. but a few questions first!
are you paid weekly or monthly?
is the 140hrs allowing for training / annual leave too?
my first thought is that you have to "forget" which day of the week the roster starts. I think it may be better to think about the culmaltive hours for the month and place them in that way, so some weeks you may do a bit more or a bit less but the hours are covered.
most of our staff work 7.5hr shifts which fit nicely into the weekly roster (BTW ours is a sunday start date but thats a traditional NHS thing!), but our night staff do 10.75hrs per shift, this fits better into a two week pattern. staff tend to do 7 on, 7 off or 4on, 3off, 3on, 4off. This also gives the flexibility to staff to extend their holidays (7nights, 7 off, 2 weeks leave) - this is a real hit with our teams.
I think an 8wk roster is too long, 6wk is better to work with, but good practice is to always have four weeks published. Its also good practice to open for requests and close these on the day the roster is to be created for that period is closed. I can get my hands on a roster publishing calendar if thats helpful to you which is based on the 4wk model.
One of the major issues is trying to fit these in aswell as things like flexible working requests that have been honored (you may not be privvy to that info but with such a small team you probably know anyway)
You say that for 2wks in 8 you don;t achieve your contracted hours. Are you still paid for this?
can't think of anything else at the moment but theres some food for thought for you.