So if the voltage drop is the same for any wire, why use 24v over 12v?
assuming the load is re-designed to do what it is doing at this higher voltage).
I think this is what I was missing?
Yup, that's it ...
In looking up 2835 series specs I found that 600 LED 16 ft light strips (
like this from Amazon) using 12 v 5 A power supplies are common. Is that what you have?
If so, just because it recommends a 5 A supply does not mean the LED strip actually draws 5 A. Do you know what that actual draw is?
Also, many of the power supplies recommended for with SMD LED strips are constant current devices, controlling their output voltage as needed to keep the load current within specs which adds another twist to you situation.
A somewhat exaggerated example is the
30 W UV LED I recentlly used in a UV curing oven I built from a salvaged microwave oven. It uses a
constant current 18-39 V power supply and draws 900 mA at 33 V from same. The supply is capable of delivering up to 39 V (if the specs are valid) so I could place the LED 520 feet away using 18 ga. wire. The power supply iwould then deliver it's full 39 volts; the drop across the wire would be 5.96 V; leaving 33.04 V to make the LED happy. It would not be an especially efficient way of doing it, but it would work
Putting these numbers into the online calculator validates this:

If you are indeed using one of those 16 ft LED strips, you might want to do some empirical testing. Get 15 ft of 14-2 w/g Romex ($7.55 at Home Depot), hook it up (you won't even need to take the wire from it's plastic bag) and see what happens,I suspect it will work fine--you'll lose 0.7 V in the 14 ga. wire but that should not have any major effect on the LED output...