I have decided to paint on wood instead of card. My pieces are still the same size 148.4mm X 105mm. Everything is done by me including cutting and assembling the framework behind the painting.
Painting on an inflexible surface is more challenging but I am able to create more depth into the painting. I am still using my trusty iron, but now also a heated pallet to melt the encaustic medium and mix in the pigments. With also painting the wax on with a brush, I use a heat gun to fuse each individual layer to previous layers.