Mine has the same factory mini starter it's had for 10 years. I also had trouble starting hot. Locked timing at 35, 13-1 compression. The wiring (2.0 cable) was voltage drop checked. No issues. It had 2 optima 850cca batteries. The small alternator couldn't keep up with the fan and water pump load. The voltage wouldn't be at full charge (12.66 volts). Went to a a single 675cca 16volt battery. Everything else is exactly the same. Never had an issue since. You can have all the amperage in the world. Starter winding resistance goes up with heat. as stated if the full battery voltage isn't making it to the starter it'll cause issues. If the battery is down on voltage (12.00 volts is only 50% state of charge) it's not going to crank hot.
Doug