In the fluff for certain psychic abilities, it implies that particular psychic attacks may overpenetrate (blood lance). When fighting a horde, since these abilities do not state that they do extra damage to horde magnitude nor do they attack multiple times, do they only do 1 point of magnitude damage on a successful use? It doesn't quite match the imagery described in the fluff.

Since armor and cover bonuses apply, I have made this house rule as a stopgap: Blood Lance does damage to the horde's magnitude EQUAL TO THE ATTACK'S DAMAGE VALUE DIVIDED BY THE HORDE'S LISTED ARMOR POINTS + COVER PROTECTION. Does that sound like a plausible solution? Did I just overlook something in the rules stating that powers like Blood Lance do more damage to the magnitude of hordes?

Per the horde rules on pg 359, all psychic powers do Psy Rating damage. If they are area powers, they do an additional 1d10 hits. Overpenetration is not covered, or else it would apply to a lascannon as well (That blast would vaporise a nice long path in a horde of packed termaguants). Lascannons are specifically mentioned at being poor weapons vs a horde, thus Blood Lance would not have any additional damage beyond the Psy Rating damage.

Rethinking, Blood Lance might count as an Area power, but it does seem that a lascannon should be able to do similar damage.

Thanks, I must have missed that. That is probably an amount of damage around the same as the average would have been using my method anyway!