Catching them as they concentrated on arrival in Normandy is another matter. On the 6th, 7th, 8th they suffered badly from conventional air attacks when moving to the assemblly sites.
By the time the it is clear the pocket cant be closed with ground forces the narrow neck would expose the Allied soldiers to the detonation. Pulling them back five or ten kilometers would allow a lot of Germans soldiers to rush out before the device can be deployed.
With the advent of nuclear artillery circa 1953 such a tactic would be practical. A local army or corps commander would be responsible for the exact timing and other coordination once the weapon is released for use by the theatre commander. The lower yeild artillery munition would not require a huge safety zone for the blue team.
How concentrated were was the German armoured reserve force prior to D-Day. ...
Probablly too dispersed. Conventional air attack in the previous months had forced increased dispersal. As I mentioned early some of the artillery battalions in Normandy were removing reserve ammunition from the battery positions - back to protected sites.
The mention of Falaise reminds me of another bit of trivia. The area near there was the primary cluster of supply depots for the 7th Army. IIRC most of the mechanized corps/divisions arriving were routed through the area to refuel and draw and ammunition or other shortages before heading into the battle zone. A nuclear detonation over this cluster of supply dumps lat on the 6th or on the 7th is going to disrupt the 7th Armys ammunition supply and possiblly catch a Pz Div refueling.
I dont think this is classified any longer, but here is a priority target list we used for choosing targets for nuclear weapons back in the 1980s. It is not set in stone & they varied from one situation to another. It is food for thought in discussing operational or tactical targets.
1. HQ, key communications centers, command knodes
2. Nuclear weapons, chemical or biological weapons
3. Supply dumps
4. Critical service or support sites
5. Combat reserves, attack forces assemblying
Command elements were invariablly at the top of the list, tho NBC weapons deployed for use would likely jump to the top for imeadiate action. The list is not much different from the priority list we used for conventional artillery or air attacks.