How to right or left shift function on a semi-logarithmic scale?

Question

I am reading a paper where the horizontal shift of sigmoidal functions is explained by the division of the function by a constant. Here the functions:

I assume that this is the case because the data is plotted on a semi-log scale, as else functions are horizontally shifted either with adding or subtracting a constant from $x$: $f(x+a)$ or $f(x-a)$.

So my question is, why is this shift achieved by division on a semi-log scale?

Original paper, the posted plot corresponds to Figure 2b.

Answer 1

If you look at the horizontal axis, to move one unit to the right you multiply by $100$. On a standard scale you add one unit to move one unit to the right.