Valuation, for this purpose is calculated as the lower of floor price or adjusted last sale. This is limited at the lower end by the current collection floor.
Adjusted last sale is the last sale price, reduced by 25% for sales 1 year prior, pro-rated between 0-1 year and capped at a 25% reduction.
Valuations are not calculated based on items which are flagged as suspicious on OpenSea.
A fuzzy has a floor price of 7 ETH and a last sale price of 6 ETH. The sale was 6 months ago, so the adjusted last sale price is 6 reduced by half of 25%. 6 x (1 - 0.25 / 2) = 5.25 ETH.
A bold has a floor of 20 ETH and a last sale today of 25 ETH. The valuation is 20 ETH.
The last sale for a slinky today is 4 ETH but the collection floor is 6 ETH. The valuation is 6 ETH.