Annuity vs interest-only puzzle

This is wrecking my head.

€1,053,122 mortgage balance with 27.66 years remaining.

Annuity repayment was €5,769 per month at 4.85%.
Came down to €5,461 at 4.35%.
Reduction of €308 per month.

But 0.5% of €1,053,122 is €5,265.61 for a year or €438.80 per month.

I know there's an effect of paying a small amount of capital off each month (~€1,600 per month) but that's very small in the context of the overall loan.

So why did the repayment not come down by over €400 per month?

Karl Jeacle's calculator doesn't really help here.

You are paying off the entire loan over 27.66 years.

The saving from 0.5% amounts to €438pm in the first year and is still over €400pm by the 5th year.

As time passes, however, the capital repayments gradually become a larger proportion of you repayments, eating away at the outstanding balance.

By the 14th year you've knocked about €300k off of the capital owed so the benefit of the 0.5% cut is less than €300pm.

From the 25th year on the interest saving resulting from the 0.5% cut will be under €100pm.

The €308pm is simply the level amount that equals present value of the interest reduction over the total remaining lifetime of the mortgage

Thanks.