Screwdriver and conductive foam turned up this morning so I sat down and got to work with the fix.
My issue with the left joycon was cutting out and short desyncs from about 4-5 feet away made worse if I rest my legs up in front of myself, level with the switch on my desk.
After adding the foam and giving it a test in the same relaxed position so far it's been rather flawless and i've not noticed any cutting out while playing fast rmx, I also tested it's overall range playing the switch at a room size distance away, perfectly fine is nothing is in the way but behind my back it was jumpy, however both joycons were doing this so it's a limit of the tiny wireless packages in the joycon mostly.
It's an improvement for sure but it's not as good as a revised joycon motherboard would be, having the built in antenna lead up next to the metal casing of the analog stick is just bad design from the ground up.
Overall I paid £3.39 for everything, 0.99 for the screwdriver and 2.40 for a sheet of conductive foam just so I could cut a small square out of it.