Rafal - You know, I just read your last post, and you are doing something I've never done in the past (or seen done). You use a much thicker protective layer between the platen and the print than I ever have (4 ply). When I was dry mounting, I used only a sheet of dry mount release paper (sold by Seal at the time) between the print and the platen. This is a waxy feeling paper that is smooth and somewhat glossy on both sides, and will not stick to the tissue. With this, you don't have to allow for temp differential. I actually made a large folder of the release paper, the size of the platen.
I used about 210F for about 25 seconds (3 min + seems very long to me) with good results all the time.
I also pre-heated (to drive out moisture) both the print and the board).
Then tacked the tissue to the print.
While the board was being pre-heated, I trimmed the tissue to the edges of the print with a razor blade.
Then I tacked the print to the board, then put it in the press.
This was with MT-5 tissue and fiber paper. You might try release paper instead, without adjusting the temperature.