Can you tell what are the other factors?
All I know adding more layers increases resistance by some number (the diameter of more outer turns increases), so R losses increases.
The next is decreased coupling factor since middle distance between primary and secondary increases.

There is a significant difference in efficiency between EI core and the Toroidal transformer. the losses are much less in Toroidal due to the magnetic field retained in the core, also the turns ratio is far less in a toroidal version.

 

There is a significant difference in efficiency between EI core and the Toroidal transformer. the losses are much less in Toroidal due to the magnetic field retained in the core, also the turns ratio is far less in a toroidal version.

How can turns ratio be separated from the voltage ratio?? or is that not what you meant?? You really got my attention with that statement!!

 

Turns required per volt, EI is typically 4 to 5 turns/volt.
Toroidal, ~ 1.5 to 2.5 , typically.
Turns to voltage ratio.