A few things...
You might add AMMONIUM THIOCYANATE to the developer rather than exhausted fixer, it may work better. You should check this thread out http://www.apug.org/forums/forum205/...rotypes-2.html
You also might want to thin your emulsion. The last time I made dry plate tintypes I mixed my emulsion like this
15ml Ilfotol solution (or properly diluted photo flo)
15ml Everclear Alcohol
45ml HOT Gelatin Solution
You may not need to thin it so much, I'm actually spraying the emulsion on which is an awful way to do it, but I do get nice even coats, which I've never been smart enough to achieve any other way...
Good Luck! Your images look nice.