standard shrinkage is deginated by AATCC which is global standard.
Based on standard, 100% cotton jergey is 5-7 % is best result.
For example pacific sports size XL length is 30.5"X 6%= 1.83" shrunk is normal.
This shrnikage is coming from natural cotton staple shrunk mostly.
Usally, varience depend on cotton growing location, 4-5 % shrunk on cotton staple on 1st & 2nd wash with tumble.
Temperature of tumble dryer is also varience factor, max temperature is 2-3 % more shrunk than moderate, but it's relax within 15-20 min when shirts cool down,
and cold water & hot water is varience factor as well (1-2 %).
So need to check carefully and make judgement is best way, I think.
pacspo use only USA grown coton yarn only which is one of best quality in the world, it's says 4 % shrink on cotton staple.
If you test warm water(40-45 F) and moderate temp on tumble and measure 10-15 min after, I believe you will get same result.(around 6 %)