Breaking in Tall Boots With Elastic Panels

I never expected to have this much trouble breaking in a nice pair of boots, but I thought I would ask for help!

I bought a pair of Deniro Salentos a year ago and they have never broken in through the calf. I did the hot water method, which made the foot become the comfiest thing in the world, but the calves are still painful until the end of my ride.

I can zip no problem (and wrap my fingers around the zipper to pull it up), which makes me think maybe the elastic panel is giving instead of the leather stretching. Any tips on getting the leather part to stretch?

Have you tried the Der Dau boot stretch? https://www.smartpakequine.com/pt/pt/der-dau-boot-stretch-8999