Well, if you measure it like that then you dont have a controlled environment, meaning if you have a drop it may not be the mods fault and actually the attys fault.
However, i did something similar, i put my AGA on my VAMO, fired it at 3.7V, meter the AGA, then put it on my mods, put in a battery measured at 3.7V, fire and meter the AGA again. I got the same number. Thus, i can conclude that the mod has no voltage drop.
And to be honest, even if there is a drop, if its performance satisfies you, then it doesnt matter. So dont let it get to you.