If it won't hold boost, you have a leak rather than a spring setting wrong. What you want is it to operate as fast as possible, dump the excess (and only the excess) boost, and close up.
So you start soft and work your way up, listening when you take your food off at WOT (it will flutter all the time at partial throttle, not an issue) for a nice clean vent. Go stiffer. Still clean? Stiffer still, until you hear flutter of any kind at WOT. This means you are stalling the turbo, so back off to your last good setting and have a beer.
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