Argyrotype exposure

OK...right about now, you're all probably tired of my argy posts ;-)

Just trying to nail down the process and variables...

For those of you who use the sun (and I know there's a whole pile of variables in there alone), what do you find is a good exposure time for a nice contrasty neg with a DR of around 1.9 - 2.0?

I've tried a few different things, but I also think my sensitizer isn't holding in the paper like it should, so I also need to get some Tween.

I expose my argyro about 20% more than my platinum ( if I toned them in platinum/gold or palladium before fixing) if not I expose twice the time I need for a platinum. My platinum timing for is around 5-8 min. depending on neg.