Thanks,
Yes it was the description that was confusing me a bit. 'Part or all of a feature' makes it sound like it is somehow using the centroid to grab features that are partially contained.
After testing different relationships in ArcMap I see that my assumptions are wrong, and it is the Intersect that I want to use as suggested. Although because my input geomerty uses coincidental lines as my select layer (but maybe not topologically perfect), this will select external polygons that I don't want. I ended up running a negative buffer on my input geometry before the final query with Intersect.
thanks again