Many forum members ship their large corms through
USPS that are cut similar to the one I have in the photo.
We do this to save on shipping costs
Like yours it is cut close.
I have never used
John Innes#3.
It could be little "heavy' for your purpose.
Take a moment and look at the
soilless mix I use and see if you can purchase or make something of similar lighter consistency
Like Louis14 said The plant will take a bit to sort itself out especially since winter is coming.
Good luck with your plant.
Orinoco corm by
Hostafarian,
on Flickr