How geographically seperated are the sites?
At a previous employerer we implemented a H&S super-committee, which had oversight of the site H&S committees and helped provide both guidence and consistancy. The site chairs and respective mgrs attended the oversight committee, which all risk registers etc funneled into - this decreased the difference in subjectivity of risk.
We found that there were still true site-specific differences in both risk and approach that needed to be taken into account.

I'm interested in how risk is seen as different depending on location. If you have the same hazard on each site, and you manage it in the same way the risk should be the same. And hopefully irrespective of having a committee or not.

'm interested in how risk is seen as different depending on location. — Andrew

Perhaps they are considering the number of exposures to that risk Andrew, site A uses process XYZ several times a week, and site B only uses the same process once or twice per month

In our case, some of the site specific risks were not internal.
One of our sites shared a boundary with a fuel tank farm for a major port - since our major activities included welding and gas cutting, the fire risk was seen as higher than an equivilent site next to a sports field.

Yep, our traffic management is different site to site. Same fundamental hazard, but extra location-specific risk loading and some different (additional) controls needed.
The people who work at each site will pretty quickly tell you how their site is different ;) Then I guess it is a case of setting the minimum requirements, which may be above what they think :)