Having fun pushing the limits of the Tokina downtown the other day... If you let the lens tip back a little, like this first shot, things start to go wonky fast, but no worse than any other UWA I've seen.
Better off using the levelers in the viewfinder of the K1 which are a big help. Shooting straight and level like the second pic is the real answer, but that is not always possible.
Pentax K-1 Tokina ATX II 20-35mm F3.5-4.5 ƒ/7.1 20.0 mm 1/640 iso125
Pentax K-1 Tokina ATX II 20-35mm F3.5-4.5 ƒ/7.1 20.0 mm 1/640 iso200
Pentax K-1 smc PENTAX-DA* 300mm F4 ED [IF] SDM ƒ/6.3 300.0 mm 1/320 iso1250