When reviewing goverment grant proposals I am not allowed to review anything coming from the same university, even if I work in a completely different departmen

When reviewing goverment grant proposals I am not allowed to review anything coming from the same university, even if I work in a completely different department/campus etc. same goes for conference reviews, but somehow if there is much more money involved the rules don't apply anymore? Generally the rule for declaring a conflict of interest is not if you think that you have a conflict of interest, but if your role could be perceived as a conflict of interest. I would say this is clearly the case here.