If It was mine I would try removing the existing fan and mounting plate, install a belt driven fan and test.
That alone should improve it, going down the road (but it will still heat up at low speeds due to the lack of a shroud).

I also used to use a pretty high antifreeze to water percentage (Michigan freeze protection) but went to 50/50 and
noticed a slight improvement. I'd suggest that later as well unless you're dead set against it.

A deeper shroud as mentioned should also improve it at low speeds, but if you look for one, try to find one that allows an airflow path for situations
where the car is moving 50+mph (as airflow through the grille from a car moving 50+mph is better than most any fan could provide).
Many aftermarket E-fan/shroud combinations don't have those provisions, and the fan usually ends up running constantly at higher vehicle speeds when it shouldn't be needed. In fact the fans can move slower than the air coming in through the grille, and potentially block some airflow.

Once any improvement is found, then the crossroads question is usually whether to revert to a more OE setup with belt driven fan and custom shroud, or stay with electric
and try to find a shroud with louvers or flaps that open at higher speeds and allow airflow.