Does Section 4.2 in the following document help to explain an Hp(0.07) dose of approximately 230 mrad/h compared to an Hp(10) dose of approximately 2 mrad/h?
The answer is very simple. You should calculate the surface beta dose rate of slabs with different thickness. Due to the self-absorbtion, the contribution of the "back side source layers" is decreasing when the thickness of the beta-radiating slab is increasing.
Note: the use of R (röntgen) is not conform with the topical ISO standards.