Need help to provide timing constraint and understood the working of Timequest

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There is a danger when using false paths across domains like this that, in theory, the fitter could place the CDC registers on opposite sides of the chip, which would be a problem.

Often it is better to use a max delay instead of a false path. Something that should make it easy for the tool to route but not do something stupid.

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yes I have heard of that, and too much delay affects MTBF. However the tool detects synchroniser chains and it should be their responsibility not to put the registers miles away but yes I will use max delay instead of false path.