Policy Statement on Address Space Allocations

Unless you announce both the /16 (or 19) AND the /22, they are not
multi-homed but only single routed (with some fallback for those who see
the /22 announcement). Anyone who gets the unfiltered /22 announcement will
used the other provider (so long as that provider is up) while you get used
only by those who get a filter routing (and as fallback when the other
provider goes down).