We're in a "variable reception" area for Ridge Hill mast, about 20 miles
away. The Humax STB reports a very weak signal on most channels but the
picture is OK for much of the time - the boss would like it to be OK all
the time so I need some advice.
The current aerial is a 16 element Yagi, with a masthead amp and newly
replaced Webro WF100 cable; all connections are good. The house is tall
and the aerial is on a 1m'ish mast attached to a tall'ish chimney
(worryingly, a bit above the lightning conductor!).

It looks like I need to replace the aerial with a higher-gain type so
I'm wondering whether to go for a group A multi-boom type, a Yagi18A, an
XB16A or ... ? Also, the attic has lots of headroom (about 9 feet in the
centre) so, with a higher gain aerial, I'm tempted to try it in the
Attic to make life easier, but have no idea what attenuation the block
walls might cause(?).
All suggestions gratefully received.