I've done a similar recipe to Bryan's but with a bit more dark Munich than light. When I go 50/50 it was too light colored and needed more carafa to get 15 SRM. Too much carafa can give a slight roast or even ashy character so I opted for more dark munich.
I never used the Sinimar but I have some now and going to try this weekend. I'll probably forgo the carafa and just use straight Sinimar, still trying to figure out how to calculate how much.