Comparing the roads shown on the map drawn in captivity from memory by Capt. E Jones of the 2nd Glosters (taken from his diary) with modern maps the D11 leads out of Cassel towards the west, with a double-bend to negotiate a steep hill, leading to Calais and Gravelines. Shortly after the double-bend the D52 splits off to the right going north to Dunkirk, indicated as L'ANGE on this map. Another map in Capt. Jones' diary shows L'ANGE is where the D11 to Gravelines crosses the D338 from Wemaers Cappel to Haeghedoorne, this latter road being 'Route de l'Ange' on modern maps.
One thing on that map that does not tie-in with today is the reference to 'Villers Capel and Calais' heading left. This has to be an error and should be Wemaers Cappel (on the D11 modern maps), shown as 'Weimirs Cappel' on this drawing by Col. E. M. B. Gilmore of 2nd Glosters.
That aside, it puts the 'Villers Capel and Calais' road on Capt. Jones' map as A on the modern map, the branch to the right ('Lange') at B, the St Omer road at C, and the 'Dunkirk Cassel' road at D. The farmhouse occupied by 10 Platoon of 2nd Glosters will be at E. Immediately south and left of that, on the sharp left-hand bend, is shown an A/T gun at H, and a little further along the road from that a road-block before the fork in the road. Two more guns are shown at J where the D933 road to St Omer splits off from the D11 to Calais. Given that Harry makes reference to the road, a road-block, a ridge, and a farm that had been occupied by 2nd Glosters where he bagged his fourth tank, There is a distinct possibility that the A/T gun position on Capt. Jones' map - 'H' on the modern map - is where Harry was. Google Maps show it as a good defensive position on a ridge (centre of picture, shown up well by the low sun), with clear views across the plain for miles. It's true that the farm occupied by 10 Platoon would have been to Harry's right and not the left as he says, as would Dunkirk ("seen burning in the rear"), but the only other A/T positions marked are much closer in to the town, at J. This position would put Dunkirk and Calais behind them, but with buildings of Cassel blocking the view towards the coast, although maybe what they were seeing was the smoke above the buildings behind them. Today there are walls on the left (which Harry mentions) both before and after the junction through which one would have good views of the plain. The orientation table at the Wormhout massacre site shows German attacks from slightly east of South in the direction of Le Rietveld and Cassel right round to Esquelbecq in the North East, so Cassel could have been under attack from almost any direction, as indicated from the defensive positions on Capt. Jones's map which cover every direction apart from North-East. Harry mentions repositioning, and moving from being in the area of a second gun back to where they had previously seen action, which points more towards position H. He also mentions a French 75 and there seem to be two on Capt. Jones's map - one between the two A/T positions on the Calais/Gravelines road and only 100 metres from H, the other further down the St Omer road about 400 metres from J. As Harry mentions two of his crew were carrying ammunition to the gun, the former is perhaps more likely.
Sadly it is very unlikely we will know for sure, as the main part of the 53rd seems to have been east of Wormhout, and both Major Cartland and Mr Hutton-Squire who would have known the details were both killed immediately before Harry's capture.