Dani -- this is what I think might happen: the engine runs on different fuel enrichment depending on what the coolant temperature sensor is reporting. It needs full enrichment for a cold start. Since the block heater probably doesn't heat the coolant uniformly all through the engine, I wonder if the computer thinks the engine is warmer than it really is, so it doesn't provide enough fuel enrichment for that first start on a very cold morning.
Even so, there's an overall benefit to using the block heater... personally I would always use one when I have the chance. Even if it means 2 tries.
Battery warmer would help if slow cranking is the problem. But it doesn't sound like that's the issue.
EDIT: I may copy your comments to the block heater thread, too.
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I've had a lot of fun this winter (cross-country skiing, snowboarding, skating).... But I'm ready for this one to go away.
Fortunately (!!!), the long range forecast shows this weekend is probably the last time we see the really cold temperatures (eastern Ont). Goodbye -20C during the day.
Bon weekend! Have a good one.