What is the size of your company?
Is there a laid-down organization chart or hierarchy? In smaller organizations, say less than 100 employees, HR heads may report to the CEO directly. Also, sometimes there is direct reporting to the COO, Head of Legal, or other business functions—generally in small- to mid-size organizations where there is a small HR function, but the top officer is someone in a business or functional control of daily operations. It all depends on the organization's structure.
Was it always the case that the HR head is asked to report to the GM Sales? The HR Head is not on par with the GM (sales) position-wise. You will have to analyze practices and precedents in the organization before trying to make changes. Change will have to be justified in the organizational interest. By letting you report to the CEO or Chairman, etc., how is the organization benefited? You will have to prove your thesis by figures and the effect on the ground. So, make your moves very carefully and with full knowledge of what exactly needs to be done.