Health-insurance FEE ... strange charging-system

Dear moderator, if this posts is in the wrong forum, just change to correct one - thank you .

Hi,
can anybody please explain the following …

I used to pay the monthly premium (650 NT$) during the time I studied chinese at an approved
school. I changed my Visa to Joining-family-resident. I am still studying chinese, but I study less those
2 weekly hours now, as I am not dependant on the minimum weekly classes anymore (anyway) …

I don’t work (concentrate on studying), live from savings right now and my taiwanese wife is currently
bringing in our household-money.
She is doing more than the taiwanese average work-income, so her premium is about 900 NT% per month.
Roughly 50% more than I used to pay. Her job is also at a highrisk place, concrete in a hospital …

I have to insure myself on her name. We tried to insure me on her fathers’ household-regristration
(we don’t have our own household-regristration), but that way was quickly rejected.

The point:
The state-health-insurance-office told us, I have to pay the same premium as she does. I don’t care about
this 250 NT$ extra, but I just wonder why and for what reason ??
I will work here later, making my own money. If that would be average, I am back to the 650 NT$.
Our household is then making more money, and the state-insurance is getting less premium from us ??
Sorry, this logic I just don’t understand …

Last a therorethically question:
If I would not work, and we have children, would this ridiculous rule also apply for a child ???

Thanx for your helpful (do they told me a crap??) answers and your comments …