[thecatspajamas]

Do some experimenting of your own with listing similar cards at Auction and then at Fixed Price with an asking price that you think they "should" sell for, and I think you will answer your own question. Or just look at completed sales for similar cards listed at Auction vs. Fixed Price. Unless the item is both RARE and POPULAR, the Auction price realized will rarely measure up to the Fixed Price sale, though the Fixed Price sale may take longer to turn over.

There are simply many more sellers willing to take their time and fish for BIN whales than there are those who chum the waters with 99-cent Auctions.

Edited to add: I'm not sure if that addressed your question or not. Another factor may be the confidence that sellers of T206 cards have that multiple bidders will turn up their item in a search over those selling N172 cards. Generally speaking, if I don't think there will be more than 1 or 2 bidders who find my listing, I'm not going to risk running it as an auction.