All the lots weren't equal- yes you are correct.
The efo category on eBay
is bifurcated into two uneven groups. A very small set of sellers of no reserve auctions (~1000 items in the section) who are trying to unload fast. The second is a few dealers/sellers with high markup items, particulaly on non cat varieties, however cat items are like 75%+ cat. (13000-14000 items in total). These folks are in absolutely no rush and couldn't care less, generally speaking about accepting an offer unless it's within 10% of asking.
The no reserve auctions are almost entirely NYstanps or CK stamps, Even the efo dealers are using these guys to source their material, sure to difficulty sourcing material. Those I'd say yield close to the price these offerings went for.
The other 13000 items are then priced at high multiples creating a very static long term listed market. If you bought these Kelleher offerings, you can price your wares, even slightly less than your next nearest competitor and rip through inventory. Any lots that get listed at lesser multiples get sold in short time
Do I think every stamp can hit 5x or more? No, but I think many can hit 7-8+ and average out 2-3x for sure. The better ones can be 10x or more.
I think if you look at completed items outside of the no reserve auctions, you would be shocked at the prices people are paying for this stuff. Only the worst material needs any sort of bundling in this category, and you can almost always add a decent one with the fodder to increase the appeal at a multiple to force push the lot out.