I have 2 probes in my engine bay. I positioned one between the hood and top of the engine but not touching either the engine or the hood. The second one I positioned near the battery. I've moved second one around to different areas of the engine bay but not as high as the first one to git a better idea of what the temps were in the engine bay. The key is gitting a baseline fer those areas so you will know how much the temps are rising when you are doing yer grill blocks.
Ideally...the more data points/areas to monitor would probably best depending on yer grill block setup. You could do that with a few digital meat thermometers.
Yes...I also monitor my outside ambient temps with another temperature monitor as well as the actual coolant temps reported via ODBII with the Ultragauge.
Obviously the temps rose to the top when I was sitting still with the engine off...as high as 178°F. I know my baseline is around 130°F traveling at 40mph with a 67% grill block in an ambient temp around 80°F.