http://www.trawlerforum.com/forums/s6/bw-velvet-drive-question-35105.html
See the above thread, it was just discussed a few days ago and will answer your question and some you haven't thought of asking.
When do you check the fluid in the transmission, when the unit is cold or after running and hot.
There is a Velvet Drive operators manual in this Forums Library (Tab in the upper right corner of this page, manuals, page 2) which you can download and carry with you for your reference. Be sure and read page 13 in the manual about oil bleed down from the oil cooler.
http://www.hyvair.com/pdf/hydraulicfluid.pdf
Looks to be around a 4 to 5% volume change over 100 degrees. So, for a simple rectangular container, that would be a 5% increase from the bottom of the pan (not the end of the dipstick).