I just realized that the new Funko 3-packs have the same dimensions as two regular Pop boxes side-by-side, meaning you can slip two Pops into a 3-pack protector and they'll fit perfectly!
Size comparison of all Pop sizes as of now with the newly announced 19 Inch Batman : r/funkopop
Amazon.com: Acrylic Funko Pop Display Case - Fits 6 Regular Size Funko Pop Boxes, Even When in Soft Protectors [Compatible with YouTooz Vinyl Collectible Toy Figures] - Funko Pop Display Shelf :
Funko Pop Box Dimensions - 4"6"10" Inch Pop Vinyl Protectors
Funko Pocket Pop Mini Pint Size Heroes Fortnight Advent Calendar Figure LOT 20 | eBay
Pocket Size to Life Size Funko Pops! (ft. Lamarr Wilson) - YouTube
3-Pack Funko POP! Protectors Original Larger Size made with SCRATCH & – Kollector Protector
Funko Pop Box Dimensions - 4"6"10" Inch Pop Vinyl Protectors
these two pops are the same size even though one comes in a 4” box and the other in a 6” : r/funkopop
Funko POP! Deluxe Star Wars Duel of the Fates Pop Protector Size CONFIRMED by Display Geek– Display Geek, Inc.
Funko Pop Batman Blue (Giant) Jumbo 9" Inch Super Size Rare Vaulted Classic DC U | eBay
Amazon.com: Funko Pop! Marvel: Captain Marvel - Captain Marvel Holding Lunchbox, Multicolor, us one-Size : Funko: Toys & Games
Standard Size (single) protective cover for Funko Pop figures - TWalley