Mies van der Rohe chair

Hello,

I just read in your book that the Mies van der Rohe chair forces a tucked pelvis.  I only got the chair recently and did start to feel tightness in my back after sitting in it for awhile.  Is there any adjustment that I can make to be able to sit properly in this type of chair and lengthen the spine vs tucking the pelvis?  To avoid compressing the spine do you recommend any maximum amount of time that you'd sit in the chair for without getting up?

Thank you!