How do these work if only a 6 inch stub sticks out of the roof ?

To get a decent FM signal indoors I need a dipole of some sort
that is about 59 inches long, plus reflector and director.

I ask this because I am getting interference on 88.50 Mhz
from Rowridge, but not all the time. Earlier today it
was bad, but the other BBC FM stations were not affected.

When I drove into town, FM R2 on my car radio was fine,
but I don't know what transmitter it is picking up. No
interference at all. Strange.

I am midway between IOW and Wrotham.