During winter I tried to protect plants well with Frost Fleece.
I have a Non-contact IR laser thermometer and went out with it early one day measuring surface temperatures as I walked. I observed differences in temperature on the soil by as much as 12C. Some well covered plants had 10C under the fleece compared to -2C in low open areas.
I now know where frost is most likely to appear.
I also put big soda bottles filled with water next to small plants. A piece of Black Plastic in the water raises the water temperature by as much as 6C as the sun warms it ! compared to bottles without. Bottles are put under fleece protected plants in late afternoon. The fleece cover must not have open spaces as heat escapes easily. This helped a lot to protect plants from frost.
I also noticed that the frost appears just before dawn.