I do see a problem with a convex iron - if you squeeze out the melt all you're doing is heating the wax's antifriction additives and pressing them into the base 'dry'.
This statement makes no sense to me at all. What may be needed on some irons and what I had to do to the Toko iron would not create a convex shape.
No one said it would. I was responding to @bsather 's hypothetical rockered iron shape.