I have also received screws that are too long with a heatsink that was recently bought in Poland (PD: 2019-04). Looking at your nickname it is possible that we bought it from the same distributor 
so probably a bad batch.
I worked around it in a similar way that @stuartiannaylor did. I put a 1mm copper pad on the cpu package but did not put any washers as I do not have any fitting right now. Now the only point of support is the cpu package and the screws are carefully screwed to make a best balance but the overall solution took some time tweaking and is surely not optimal from mechanical point of view
I also bought an acrylic case but it turns out I cannot use the top part of it with large heatsink on the bottom.
It would be good if someone at @radxa looked into that and verified the contents of the packaging in current batches as there may be more people receiving large heatsinks with screws that do not fit the smaller standoffs. I am pretty satisfied with my Rock Pi 4b but agree that those little things can spoil the fun for many people.