split backstay tensioning

Hi

Can anybody tell me the answer to two questions.

1 How do you measure and set the tension in a split backstay. I know the tension in the backstay should be 15% - 20% of the wires breaking strength. But at the position where the single backstay splits into two bridle legs, it is about 12 feet up and I can't reach to get the tension gauge on. If I placed the correct tension gauge on the smaller wires of the split backstay, would the readings I require be half of the single wire 12 feet up?

2 The rig is mast head with single swept back spreaders. The lower shrouds are tensioned to 10%, and the cap shrouds are tensioned to 15%. The forestay has got a roller reefing system. There is a slight bend in the mast athwart ships between the spreaders and the mast head. the middle of the bow is over to the port side ever so slightly ( top of the mast over to stbd slightly). With all the shrouds tensioned equally, do I need to tension the split backstays to different settings.

Can someone advise me please.

Thanks