1152 is weak south of the Thames in London and night time listening was swamped by continental stations. This made listening to LBC as an AM only station an issue.
I used to find it was OK north of the Westway but not as good south of it. So much so when I was listening to it on a bus going under the Westway I could notice the sudden difference
Looking at the Ofcom data, 1152 Saffron Green has 6dB more attenuation than 1548 in an arc NW to NE of the site (sort of the area bounded between the M1 and M11). In a SE direction towards Erith, they are both at max power, the direction of fire is SSE (Towards Central London obviously)
1152 is 23kW, 1548 is 97kW, but that's to compensate for the different propagation characteristics between the two frequencies, all else being equal (which clearly it isn't !)