Bill, the RN is plenty powerful enough to contain the HSF unless a change of geography forces them to split their forces. If the Germans held Cap Griz Nez they could create a safe coastal shipping lane by using guns and mines so that their own warships could transit into the Channel. Light warships could attack through and cross Channel shipping that came within range, and could scuttle back to the safety of the minefeilds and coastal guns. They did this on a limited scale IOTL from the forward bases in Belgium. Where would the RN get the forces to cover this sudden threat, stripping cruisers and desrtoyers from the GF? And what about the possibility of a major warship or three slipping into the Channel, would the GF be weakened to cover this? How many ships can the GF lose before it becomes vulnerable to an undiminished HSF?
All of which depends on the Grand Fleet co-operating in its own destruction which is why David called it balderdash. Your whole concept depends on the British doing exactly what you want them to do and ignores any other posisble event. Lets look at a few likely countermeasures.
Coastal defense guns on Cape Griz Nez - sure, but the UK can install them as well, in Kent and along the South Coast. They did so historically and their heavy naval gun production is greater than that of the Germans. The British build more guns and bigger guns (14 and 15 inch by 1914 as opposed to 12 inch) and if needed they have an 18 inch gun coming down the pike. So in any cross-channel artillery duel, the British have a great advantage. By the way, the idea of such duels is not implausible - they happened regularly in WW2.
The British can lay mines as well - and they many more assets to do the minelaying with. They are not going to allow the Germans to lay their minefields undisturbed - nor are they going to leave those mines unswept. Also, minefields are declining assets, they require regular maintenance and "topping up" (mines get swept away by tides, moved by currents, they snap their cables and drift away). British mine technology is way in advance of German; the British were laying magnetic mines off Flanders in 1917. The British have vastly more minelaying resources than the Germans, in WW1 the minelayers were trawlers and Britain had the biggest fishing fleet in the world. So, for every mine the Germans lay to keep the British out; the British lay dozens to keep them in. Its Britain's doorstep remember.
And what makes you think that if the High Seas Fleet slips a few major warships into the Channel, they won't get sunk? We've already established that the UK can - and historically did - establish long-range gun batteries along the south coast. So, your major ships run into the British minefields and start getting pounded by shore batteries. We have an example of what happens when navies try that in the Dardanelles,. In this case, its the Germans who start losing ships, to mines, gunfire, submarine attack. If you look at a map, the southern coast of the UK is studded with naval bases (heavily defended ones at that) that could be used for submarine and destroyer bases.
How many ships can the HSF lose before it becomes hopelessly outclassed by an undiminished GF?
Sorry, but David's right when he is dismissive of your suggested "plan". It just isn't realistic.