Have you tried leaf cutting as a reduction technique? I have successfully reduced the leaf size in two notoriously difficult species, Common Maple / Acer Campestre and Corylus avellana / Common Hazel.

I cut the biggest leaves down to just slightly smaller than the size I want the leaves to be. Just a snip with the scissors so the leaf remains roughly leaf shaped. The leaves work perfectly well with the snip. But it causes the tree to back bud nicely. What's more, as new leaves grow I snip them too. Keep doing this and more and more leaves appear. Also, the snipped leaves grow bigger, too - so you may need to trim them again.

Just keep snipping them all smaller. Eventually the tree produces leaves at that size.

The reason I suspect this works is that a given surface area of leaves is needed for a given size of tree. The tree is lazy and wants to make 2 - 3 leaves. By forcing it to grow 20 leaves to acheive that surface area where it previously grew 3 then that's when you programme it and pretty soon that's how it grows. I think 3 - 4 seasons was all it took on my smallest Acer Campestre.