dsydorko, that is easy to explain. we need a knowledge of the Ohm's Law and some understanding how regulated mod works.
Some oversimplified explanation:
The "natural" current which flow thru a coil (let's remember mechanical mods) is determined by
R - resistance of the coil
U - voltage
Current I = U/R is appears to be predetermined.
Also the wattage P = U*I or to exclude current = U^2/R
Regulated mod cannot vary coil resistance as it is determined by its material and geomerty, so it varies voltage.
To provide more power than natural it has to "boost", to decrease it - mod uses "buck".
Any convertation requires expences (and incresing voltage "costs" mod more power than decresing it, this is why DNA datasheets specify honest 85% for a single battery chips like DNA60 or DNA75(C). on the contrary dual-battery mods normaly have only "buck" convertor and their average "efficiency" is like 93..95%).
Anyway, the more voltage mod has to add or substract from "natural" the more battery power it will consume for this certain need from the battery, so to keep battery life healthy it is logical to use the resistance providing "natural" wattage and for low wattage we have like 1+ Ohms, while for higher wattages we need 0.4- Ohms - not to rape our mods too hard.
Take a look at this picture:

it is impossible to obtain 60W at 3 Ohms resistance as this requires 60=U^2/3 U=13V, while "boost" on most of single battery mods is limited with 7V (for example DNA75) or for newer chips 9V (for example DNA75C). This is not Evolv specific. This is just the Ohm's Law.
Edited on 12/5/2017 at 5:53 PM. Reason: