Our current History Store create configuration string is:
We should update the configuration to make it very unlikely that we'll ever use overflow keys in the history store. Probably by setting leaf_key_max and internal_key_max to the same value as leaf_value_max.
The default value is 1/10th of a page split size. The default page size is 4KB meaning that the overflow size is about 400 bytes. MongoDB could definitely be triggering that with indexes at the moment.