The band is narrow in case of single income households. In case of double income households it can be large, because income tax billing can be done together for married people, while social insurances are bound to the working place.
That means if your spouse earns significantly more than the health insurance cap, for your part of the household income the marginal tax rate maybe (depending on how much your spouse is above the cap) from the first Euro to the cap (43.200 EUR) at this marginal rate.
For the calculation of the marginal tax rate I have included employer's contribution to the social insurances.

As said above, the cap is not simply a cap. You can leave the public health insurance if you earn that much, which is way cheaper. So a single with gross income of 43201 EUR, can end up with 200 EUR more each month than a person with an income of 43199 EUR.

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