I am having similar issues and i have tried many different settings.
Without silicone cover I get an even transfer result but there stays some “glue” on top of the image. Does not look good. Re-Pressing/Fixing does not improve the result.
With a silicon mat between multi trans and heat press the glue issue is gone but the transfer quality decreases. Some parts wont transfer well or sometimes it looks as if the toner starts melting.
Have not found a continuously working method yet.