Are you leaving the hygrometers long enough? digitals take a long time to stabilize over 30 min analogue ones are faster 10 min.

I personally would not expect to see much more than 10-15% above room norms. Most who use racks keep the room at 60% temps at 80ºF. Basically a rack is a enclosure with a hot spot but isn't easily made into a micro climate. It can be done but it isn't a simple process.