To clarify my comments about spacing on finals: I was meaning staggered spacing. If the runways are too close for parallel approaches with the a/c 'side by side', then they can be staggered, at the same speed, with 2nm longitudinal spacing, but on the // runway. They would still have the required spacing of traffic ahead on their own runway, but staggered from the neighbouring one and thus achieve not lateral conflict. It would be necessary for the respective GA routings to ensure sufficient separation.
I also questioned whether this would trigger a TA on finals. the preceding traffic could be less than 3nm, but there would be no closure. The boffins will tell me.
This staggered spacing is used at some airports in a different way. There are crossing runway tracks and initial GA tracks my intersect too closely if the a/c touchdown simultaneously. ATC utilises a ghost radar picture. This shows the a/c landing on 1 runway and the a/c landing on the crossing runway to be superimposed as if they are landing on the same runway. It shows the effective spacing, nominally 2nm, between their landings.