[Amps] 10 DB increase

[kenw2dtc]

"Many years ago, an old timer (W6SDM) told me that to make a noticable
difference on HF SSB, it took +10db."

While on the subject of DB.  Many times when someone adds 10db to the 
transmit side, in an A/B test, almost no one on the receiver side shows a 10 
db 'S' meter increase, many times the receiver readings show a 20 or 25 db 
increase.  Is the major reason due to liberal non-linear metering or are 
other factors such as antenna, location of both stations, propagation etc, 
the greater of the factors?

73,
Ken W2DTC