28* initial timing for a 318? How can that be?

New Holley 750 vac sec. now 6 yrs old always read same vac on ported as on manifold/baseplate. Tech. agreed it`s not supposed to do that. something I`m not doing right? TIA
92B gave a good answer. A couple photos here the show what that looks like.
But best start a new thread. This thread is about using 28* Initial timing for a 318.