I've prepared a map showing the location of the 4th Field Regiment on the 12th July 1944.
The RED STAR shows the location of the Regiment, Map Reference 948664
If you note on the War Dairies, the Regiment destroyed a "mortar battery" that same day, I am assuming (and I may be wrong) that this was the Battery that fired the rounds into the FOP and wounded him.
The BLUE STAR shows the location of the German Mortar Battery located at Map Reference 987631
This means, if I am correct, that the FOP would have been located somewhere towards the BLUE STAR
IF (I'm making an educated guess here) the Germans were using their standard infantry mortar it would have been a 8 cm Granatwerfer 34 (8 cm GrW 34). It was noted accuracy and rapid rate of fire. Max range of 2400 meters. So the FOP was probably located within this range of the BLUE STAR. Looking at the map, I may suggest that the "woods" between the BLUE and RED Stars may be a possible location or area around their. It is approx 1,000 meters from the BLUE STAR, so the FOP would have had "line of sight" to the Mortar Battery when they fired. (All of this is just assumption on the information presented in the War Diaries, they may have been further back, but I don't believe "closer" as the country side is more open as you leave the wooded area)
For maps, see the link Below, I used the 1:100,000 map of the CAEN area
Having said all the above, he 'may" have been wounded on the 13th July. His records are a bit confusing. One record says he was wounded on th 12th July and another record says he was wounded on the 13th July. IF??? He was wounded on the 13th July he may have been in 'B' Troop, which had a gun put out of action with 2 killed, 6 wounded (one later died in hospital). Unfortunately this says "shelled", but doesnt' state if it was artillery rounds or mortars. And we know he was wounded by Mortar rounds (medical records). My guess is he was wounded on the 12th?......but just a guess from all the info presented.
You may be able to confirm "which" Troop he was assigned to by obtaining the Part 2 orders, which would give more detail on the men killed and wounded (and evacuated). These records are available at Library and Archives Canada BUT you have to go there to see them, or hire a private researcher to get you the information