GIS Calculation

I didn’t think my spouse and I were eligible for the GIS, but the stress test had GIS income in there.

So I inputted my numbers in the CRA calculator and pretended I was 70 (my husband 68), entered my expected QPP income of $30K (no income for spouse) and was shocked to see GIS of $512.20/month. How can this be?

Isn’t the max GIS of $1100/month supposed to get clawed back entirely given half of $30K is $1250/month? Is there an extra calculation for each year QPP/CPP is delayed?