https://forums.backpack.tf/topic/6033-rules-for-unusual-price-suggestions/

Pricing of Strange Unusuals

Strange unusual items should be considered completely independent of non-strange unusual items. Do not use non-strange sales to set high ends on strange items even if they sold for more than the strange one. Do no use strange sales to set the low end on non-strange sales even if they sold for less than the strange one. Treat them as different items for the sake of the suggestion.