Phil,
It's illogical and unscientific for the very reason I suggested.
If you beg to differ, then some other factors must be coming into play (with your cooking). Like size of pan, size of heat source, etc.
But, if you really believe that adding a "single portion" amount of garlic and ginger (for example) to a "double portion", gives the same result as two individual portions combined (with, therefore, twice as much garlic and ginger in it as in a single portion), then good luck to you! But please don't try and convince others of it and try to sell it as an "empirically proved fact"! :

Rather than simply saying "I don't understand this, therefore it cannot be true", why not try the experiment for yourself and then report your findings. That would surely be both the logical and the scientific thing to do
I do it all the time, Phil, and what I personally find is that if you want to make double the portion, then double ALL of the ingredients. If you want to make x times the portion, then multiply ALL of the ingredients by x.
The only caveat, in my opinion, is that, to get the same result, you must have a heat source and size of pan that are capable of replicating the same cooking conditions.