A spark plug (10) for a spark ignited internal combustion engine includes a suppressor seal pack (54) interposed between an upper terminal stud (46) and a lower center electrode (60). The suppressor seal pack (54) includes a top layer of conductive glass (52) surrounding the bottom end (50) of the terminal stud (46) and a lower glass seal layer (58) surrounding a head (62) of the center electrode (60). A resistor layer (56) fills the space between the conductive glass layers (52, 58). The resistor layer (56) has a larger first cross-sectional area (76) at its upper end and a smaller second cross-sectional area (78) at its lower end. A reducing taper (80) establishes a progressive transition between the greater and lesser cross-sectional areas (76, 78). The reducing taper (80) is located in a large shoulder region (LS) which is defined as the longitudinal dimension between the theoretical reference point (70) at the filleted transition (26) and the theoretical reference point (68) at the upper seat (17). The suppressor seal pack (54) is of the fired-in variety in which each layer (54, 56, 58) is separately filled as a granular material, tamped and then cold pressed using the terminal stud (46). The assembly is then heated in a furnace, then removed so that the terminal stud (46) can be used to hot press the suppressor seal pack (54) into a final, operative condition. The suppressor seal pack (54) has a length (SL) which is maximized by use of a positive “A” dimension (+A) defined as the longitudinal distance between the center electrode head (62) seat and the theoretical location (72) of the lower seat (19).