hello and thank you. on the plate above, I use my 1 ton arbor press. one problem people have is trying to do it all at once. That won't work.
All of the force is in the one inch center of the ram foot so pressing doesn't do much for the outer perimeters. What I do is start in one corner and press.
Move over 1 inch (the size of the ram) and press again. rinse and repeat until you've covered the entire surface. I've successfully done an 8x10" this way.
If you're looking for an easier way to spread the pressure, a friend of mine makes these for the arbor press: presser foot