I have some experience dry mounting 16 X 20 size prints onto mat board but I now need to dry mount a 24 X 36 print onto 32 X40 mat. My heat press is smaller than the 24 X 36 mat.
Normally I cut the tissue larger than the print, use a tacking iron to tack the center of the print back to the tissue, then tack a few other areas, trim the print and tissue together, position print on the mat, tack tissue to mat, cover with release paper and a protective cover mat, apply heat in heat press, remove from heat press, cover with another mat weight down then wait till everything cools down.
In order to mat the above size prints I imagine I would do about the same thing, however I am going to have to step the heat press over the print. I think it would be best to start in the center and step in overlapping steps to the edge of the print I am also going to have to do a 180 on the mat with print to cover top and bottom areas with the heat press.
Now would it be better to initially start in the middle of the top do the 180 and do the middle of the bottom, then work toward the edges.