the reason my gate is not absolutely all the way closed, is that the stove needed a little more fuel in the pot to reach and maintain the needed temp to initiate further feeding of fuel.
at the start of this season (my 4th with the stove) i had to tweak the gate till i got reliable starts again.
pellet size is also a variable/part of the equation you are adjusting for. but it's just an aspect of the basic question of how much fuel is being delivered.
the rationale is that larger pellets leave more air space in the tube so deliver less fuel per auger turn at any given feed gate setting. whereas smaller pellets pack more fuel in as they fit more closely together.
it takes a while for any adjustment of the gate to take effect. the auger tube has to refill itself at the new input rate. 10 or 15 minutes is a safe amount of time per adjustment.
small increments can make a difference. and you are fine tuning, so keep that in mind.
too much fuel will be a problem as well for flame height and vigor and air flow.
the manual instructs to set flame height while on high. but you need to be sure it will run on low as well.
of course, keep the pellet level in the hopper low enough to access the gate between adjustments. but not drastically low. you need some amount covering the tube to keep vacuum in the system
like someone else mentioned, the fact that you got pellets to drop and the stove to run says the vacuum switch is working (otherwise the auger wouldn't turn after the initial drop sequence) so my best guess is all you need to do is get enough fuel in the pot to get the needed heat to get the stove running on it's own.
you just have to hone in on it manually.
once the stove is running, it is possible to have it feed enough to run on low, but then that amount may possibly be to low to actually light from cold on low. hope that makes sense.
what the tech said is reasonable in a way, you are likely to succeed if you start on high, but i have mine adjusted so it will indeed start on low too. if it won't light on low, then you won't be able to run on a thermostat while set on low. really the stove is designed to light on all three settings.
if you overshoot a little and get the rate a little high, that is fine. then you can start backing it down and adjust flame height on all settings and then see if it also lights and runs on all settings.
you'll get the feel for it.
hopefully i'm right and what i have experienced is basically the same for you.
best of luck.
*edit to add, you might possibly have to reset the gate if you change brands of pellets. not always, but because of what i mentioned about pellet size, it is always a possibility.
What is the "cold start syndrome"?
i've never had this per se. but i imagine if your stove was drastically cold to begin with, you'd need even more heat to reach operating temp.
being as this is in your shop, that may be a part of your equation.
lol! i see you are in alberta. yeah. this is probably a factor. but it's still the exact same principle.
i suppose if it was cold enough, lighting on low
could be compromised. again, you don't want too much fuel.