I think I should point out that a sharply swept delta like the Vulcan a reflex airfoil is not a necessity. The full size did not use one.
The stability of such a delta comes from the vortices created over the wing upper surface. The more acute the delta the greater the stability.
My suggestion is to simply use an airfoil similar to the full size and then fly it like a Vulcan.
A conventional airfoil and particularly a reflex one does not work at all well as a delta for inverted flight.

I have four scale RC deltas.
Douglas F4d Skyray.

Concorde

Fairey FD2

The XB70 Valkyrie

None use a reflex airfoil and all are perfectly stable.
The only drawback with such delta configurations is that at high angles of attack, or even a steep turn, they need a lot of power to maintain it.