If I've done the sums right then if your spring was correctly 36 lbs/inch at 16.5" long them shortening it to 16.0" will make it 37.125 lbs/inch. I regard that as within the manufacturing tolerances. Shortening or packing by fractions of an inch might be regarded as tuning for the individual. Chris Launders at 280 lbs had to pack his 45 lbs/inch spring by about half an inch. I'm more than happy to get a price for making some of those adjustable length inner spring boxes but I would need to have an order from one or two people to make it worth while bothering people.