.... Changing the location of the antenna wont help in the slightest and the path will always be the same due to the location of the house and whats inbetween it and the transmitter.
The only thing i can do in regards to moving the antenna is pointing it towards tower hill (listed as Warrnambool transmitter currently its pointed at Warrnambool city transmitter)
You've provided more info in your forum post than in your PM and the answers received so far are all pertinent, so I'll reply here.
Your quote above rings alarms for me, when you say "Changing the location of the antenna wont help in the slightest".... this may be quite wrong, as even moving an antenna position even a few centimetres in any direction, including up/down, can make a huge difference.
This would be the very first thing I would be doing, searching for a more-suitable antenna location.
As mentioned, trees/foliage moving in the wind and chages in moisture content can alter signal paths, absorbing, refracting and reflecting signals.
As a result, signal may be decreasing, increasing, adding multipath signals, all of which can upset DCP, BER/MER.
Different frequencies may be affected to varying extents.
Also as mentioned, I would also be checking options like using a different transmission site. EG: Tower Hill, which has a max power of 8KW as oppsosed to Warrnambool City, which is only 630W.
I also agree cBER and RS dropped packet readings (if your meter shows RS) provide better indications of issues than just MER.
Elevation between your antenna and the TX can be an issue with antennas reasonably close to TX as often the signals can be going over the top of you, with insufficient downtilt from the TX antenna array. (I've seen this quite a bit).
Tilting the receive antenna upward often helps in these situations.
Without being there, it's very difficult to advise.... you just need to go through all the standard processes a good installer would do... the most important, is test numerous antenna mounting positions.
Testing with different antenna types... often one antenna type will work better than others... and it's not always the type you may expect in theory to work best, or the one that worked best at the house next door.