Blue tits settled in a box with hole sized for a starling

Hi all,

We put up a bird box which was sized for starling back in 2020. Since then we have seen starlings go into the box with ease but they never settled.

This year however we been lucky to find that a pair of blue tits have decided to take up accomodation in the bird box!

Bit concerned that with the hole size being 45mm they could be open to attack by starlings! Is there anything worth doing at this point or best to wait till the autumn and stick a 25mm ring plate on to reduce down the hole size?

Or maybe do nothing and keep option open to a wider variety of birds?