Ignition advanced

I try to change my question. Because I assume that my wording was a little confuse.

when the advance unit hose is DISCONNECTED from the carburetor connection I read 5 degree BTDC, and this is ok with the manual book(5 BTDC when DISCONNECTED), but the manual doesn't say what will be the igniting timing when I will RECONNECT the advanced unit hose. And when I RECONNECT it(and no matter which connection I choose in the carburetor)the advanced is rising to 20 degree BTDC!(All this checking is on idle). Does that make sense?(This is 15 degree more advanced, the max advanced that the unit can give and all of this " ON IDLE?") Does it sound ok? The vacuum advanced unit is new and original p/n. The advanced plate is move free(i mean it doesn't stuck). So what should be the advanced when the vacuum advanced unit hose is CONNECTED
car details:
opel corsa A 1389cc. Year-1990.
engine-14NV. Carburetor-PIERBURG 2E3.
bosch distributor-0237009073(HEI inductive discharge system)

i will be very appreciate for an answer.