Nick Zezovski from GME just told me exactly the same thing Plucka.
He said to get an 'all ports power pass' splitter and another psk06.
I'm not sure if there have been transmitter upgrades over the lest twelve months, but intuitively the best signal does seem to come from the direction of western end Henry Street. This changes with the weather as you would expect and it seems like the southerly signal is stronger when it's raining (the channel combination alters).
Thanks v much for your help, a relatively simple fix and affordable too. The only problem I might have is that GME Kingray seem to have discontinued their old product lines, in which case I'll have to put up with whatever replacements are available.
Hopefully will be able to get the extra pieces necessary and complete a new installation. The cabling to the current splitter is a mess, so will try to tidy up the connection, this will probably include a joiner of some sort...