In my aerospace company we have repetitive discussions regarding the stacking of low tolerance fasteners with non-countersunk washers. For example a fastner NAS6703-X (size 10) has a max. base radius of .02". A non-countersunk washer NAS1149 size 10 would clash with the base radius if modelled.
Having done a fit check, there is no clash but to avoid issues we have used bigger sized washers on some occasions. I find it odd to use different sized bolt/washer combinations.
Are you aware of any guidance material regarding this, respectively has anyone else met this topic?