support towers will not fuse in Cura need help.

as you all know I have an ultimaker S3 and run Cura. I took my time in cura and moved the support towers so they were touching the Lithophane and as you can see they did not fuse when it printed it had a gap of about .5mm
I think it is a setting in Cura
what do i need to do to fix this.

Thanks
Dale