The hourly average values of the IMF as observed by Helios 1 and 2 in the period December 1974 through March 1978 have been examined to deduce how the sector pattern seems to evolve with time and heligographic latitude (¿7.2¿ from the solar equator). The dominant two-sector pattern observed after 1972 extends to the whole declining phase of solar cycle 20, and the corresponding source regions seem to corotate with an angular velocity smaller than the equatorial one. The latitudinal dependence of the IMF polarity (sunward field lines below the solar equator) is observed, with occasional deviations, through the whole period of time and becomes particularly clear in the first half of 1977. Gross scale implications for the shape and location of the sector boundary surface are discussed.