When the slab have a biger height, the rigidity of the slab is biger and the beams can't deform.
My advise is to create a thin slab (like 7 or 8 cm ) and the diference of weight (til 30 cm) you give as a surface load on slab. I use this metod when I want to increase the ratio for beams.
Please check also:
Hope this help you understand this situation even better.