I tried flipping the Aurifil spool upside down but the thread just caught on the bottom instead of the top. I have to tug the thread to get it to release off the spool. Weird.

some machines require the thread to come off the spool from the back, flipping may not work. the Cap must be larger than the end of the spool to help. I think i heard of someone putting clear nail polish on the slit... not sure. i have an old emery board I sometimes use to file things smooth. but lettering, all i can suggest is the cap being larger.
if all else fails, maybe you can set the thread on a thread holder on the machine table itself. like we do with larger spools. good luck.