Kristopher, that's some excellent reporting there.
I don't profess to know much about these problems. I've got a couple of cars that are less than stellar starters in my mildly cold climate (I have noted that when it's down near the threshold of 40 degrees that the cars start harder- GPs not fulling commanded yet). One I'm figuring needs its IQ bumped up: this one actually fires right up, but stumbles a bit afterward (compression is good). The other is fully advanced and everything else seems fine- ironically, I'm thinking that the IQ might also be a factor here in that it's HIGH (the threads are confusing; I've read of people claiming that high IQ settings can do this, and then I've read of others stating that low IQs can cause hard starting!). For this later car I'd already replaced the starter, which wasn't spinning the engine more than about 175 RPMs (I think the new one bumped it up to around 250 RPM). OK, enough about my issues..
Compression is very important. If your car's compression is compromised then you're going to have issues starting no matter how everything else is (unless, perhaps, you get a starter that cranks 500 rpm or such!). I was looking to buy a UTV that had a diesel in it and that owner stated that it started hard; he was a big diesel engine mechanic and wasn't familiar with GPs; so, I told him I'd check his GPs, hoping that it was a simple GP issue; well, I also knew that it could be a compression issue so I told him that and he was fine with doing a compression test on it- turned out it had one cylinder (out of three) that was way down on compression.
Cranking RPMs are also key. If you're not spinning the engine at 200+ RPM (I'd prefer to see 250) then that'll be a cause for harder starting. And off course, the battery is important here! (with GPs pulling power in addition to the starter there can be a fairly substantial draw- weak battery and or cable/ground issues will diminish effectiveness).
Fuel temps. Not a lot one can do here other than run winter diesel and anti-gelling additives.
So:
1) Timing;
2) Compression;
3) Starter RPMs & battery;
4) Fuel temps.
You could verify that you have proper voltages along your GP harness. Since you're not getting any codes/CEL for GPs I wouldn't think you should find a problem here.
Can't say that I've heard of anyone having temperature-related issues with their ASVs, but since they are known to cause starting problems it's worth a look.