thanks for your helping, but I think you don't undersand what I write
1. I only focus vga 797 with Invensity 13
2. you only try to explain 795 with Invensity over 13
In MultiMiner, click Advanced and then Process Log. This will display the exact executable path and arguments being used by MultiMiner to launch either cgminer or bfgminer. If you then open a command prompt and run that same executable with the same arguments you should get the same performance. Nobody else has reported otherwise.
If that is not the case can you please describe your OS and hardware, the version of cgminer / bfgminer, and exactly how you are measuring these things?