Hi Sandy - you may have seen from a post a couple of days ago that I have just bought a new aerial. While not a radar rama, it is similar.
Prior to putting it on the roof, I tested it in the loft for a day alongside the existing supplied aerial that I've had stuck up there for a long time. Frankly, there was little difference. (Planes were at a premium at the time because of the volcano, but enough traffic round here to run a reasonable test)
Conclusion: as an indoor aerial, the supplied one takes some beating - as others on here will testify - and an outside aerial "inside" won't make much difference.
Your radar rama needs siting on the roof to get the results you want.