If you're unlucky, you do what a friend did. Crappy little French diesel pod-car, but I can't remember what sort.

Fit a Kenlowe heater, salvaged from a Disco some years back. Neatly fit exterior socket to house, and to plastic airdam of car.

Warm up engine, with timeswitch. Coolant is nicely toasty.

Start car. Badly. Chug slowly out of drive. Hit the adjacent motorway slip and floor it to an immediate 70mph (one of the reasons for wanting better starting).

After a week of this, throw it at the dealer (clueless). Throw it at the local garage. Mechanic, doing some thinking, unlike the dealer, soon finds the problem. The ultra-clever ECU is seeing warm coolant too soon, and assuming the engine is already warmed throughout. So it backs off with the heater plugs and whatever else the injection system ought to have been doing. Result - lousy cold starting, worse than ever.

Fix #0 was to abandon pre-heating.
Fix #1 was to add a switch and resistor to the temperature sensor.
Fix #2 (which I think is still breadboard and gaffer under the dash) is going to be an Arduino controlling a spoofed temperature sensor, which if it detects cold weather and the block heater having been used will then keep the "cold spoof" resistor in play for a few minutes to allow proper warming up.