I'm fairly sure the RFC did investigate defencive formation flying. During
Bloody April, formation flying was used to even out the odds and ensure that at least the more vital missions were completed (even if others had to be neglected due to lack of aircraft). Also in 1918, once the IF had been set up, squadrons of DH4's penetrated 20+ miles over the lines and back again. Maintaining formation must have been crucial in doing this. (Although then again the loss rate for the IF in its 3 months of existence was about 300%, so maybe not!)
The only specific tactic I know of was that used by FE2's: they would form a defencive circle (rather like a circle of wagons in a cowboy film) so that each nose gunner covered the tail of the plane in front. It was frequently used during the summer of 1917 when the FE2 was coming to the end of its daylight role, and facing the new Albatros types.
Regards,
Vigilant.