Do you think the way employees sit at their desks, reflects how hard they are working?

No, sitting positions would not reflect a employee's performance. And an employee who looks focused maybe cheating his employer by acting that he is working seriously.

No. I believe that the result of the job given to the employees should be the basis on how he/she did great to the task assigned. Sitting positions vary depending on the "comfortable position" of the person. Just because the person is siting professionally and focused doesn't mean he/she is doing the job well. 

no relation between sitting position and productivity.

No. Cant judge on someone's sitting position. People will sit or stand to finish their work. at the end the output with presentation skill and correctness of the data of the employee will matters to the management.

No, employees' performance should not be based on the way they behave at their desk. This should be measured through their outputs.

No , sitting position doesn't reflect how hard the employee are working,

Each employee sit at a position that he find his body comfort . 

what is important are the results .

It's not correct I guess, I am usually sitting away from my computer but I am usually working all the time. This doesn't mean I'm not working. I have seen people in the same company who do not do anything at all but are glued to their computer screens and certainly the management feels they're trying to work hard.

Yes, body language is key when it comes to the work environment.

Generally you can't  judge the way employee doing their work . it depends on employee assigned tasks and monitoring  the progress as well reviewing their KPI's

the sitting positions doesn't resulting the effectiveness reflection on hard working

It is showing how unorgnised you are/I am.

Need not worry about the sitting style or body language of an employee. Output is the MOTTO..

Thanks / Praveen