you don't have to use a "bicycle" box. stop by the motorcycle dealer and pick
up one of the boxes that electric scooters come in. much larger than a bike
box, easier to fit your large frame bike...just cut to size. you can also use
fridge/freezer boxes from the appliance dealer. unless the airline quotes
maximum dimensions, you should be okay. most only quote max weight.
[they carry surfboards and tandems...]