My suggestion would be this. Instead of programming all of the control channels into one site as it appears you have done, create a separate site for each control channel, or rather each CC and its' corresponding alternate, then assign all of the sites the same system quick key.
If you just program all CCs into one site, it will latch onto the first CC it can decode and won't go any further. If you program them into separate sites, then it will scan them all one after the other. Not quite what you wanted (only the strongest) but another option.
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