Fillet feature and spline

Hey there!

I need to create fillet features around the top face of my part and they should be around 4 mm, but the maximum I could get was 1 mm.

I know it may be because of the particular geometry, but I can't really change that shape I've got.

Is there a way I can create a larger fillet without having to change the shape/drawing of my part?

If you can take a look at it, please find attached the part.

I'd be very grateful for some help! Thanks!

SolidworksParts And Features