I am finding more and more on amps per bulb on leds do not seem to have a linear math. I am finding that, yes, LED's draw less amps, but resistance amps in cord seem to be cropping up more and taking away some of LED's power saving thunder. I have mentioned in another thread of my experience with 1100-1200 LED c-7's this year that were advertised as .56 watts and turned out to be closer to 2.3 watts each or so once you put them in 250 foot runs on a tree.
Unfortunately, just because a manu. says they only draw x does not make it so. but once installed, a fluke rms quality meter typically does tell the truth, and I would test your 1800 bulbs and get an actual reading of how many amps. my experience tells me that, for now at least, you will not get consistant readings on LED power usage on any given group of 1800 bulbs, even from the same manu.