Using Flexbond with 12 x 24 porcelain tile

I originally planned to use 12 x 12 tile and purchased Custom Building Products FlexBond. However, a change of plans…now using 12 x 24 tile. Can I get away with using what I have, or should I use FlexBond LFT? Used 1/4" Wonderboard over 3/4 AdvanTech.

Thanks