Further to our discussion, the photo paper is in the easel during exposure. I'm blocking light with white tick textured fine art paper slightly bigger than 8x10. The blocking paper is placed right on the photo paper. I don't think that the light is penetrating art paper. It is 300 gr. in weight. Yes, during the last exposure entire sheet is uncovered and exposed for 5 sec. The print doesn't look like the last segment of the test strip. It is much lighter. Today I'm planing to do new test strip and based on the outcome make another print of the same negative. The funny thing is on the test strip I can clearly see difference in all 6 exposure segments. Unfortunately I don't have scanner to upload test strip.