Professor Tonge observes dryly that "a full-blown DUP-UUP merger would be akin to that of a cat and a canary" – with the DUP in the role of a cat devouring prey.
The DUP still has a love/hate relationship with its rival party.
The main path to expansion is to continue eating into the UUP vote and support if it can, but there are bitter memories of the days when the roles were reversed.
Oliver Gibson, a Tyrone DUP veteran, still smarts from the disdainful attitude of the UUP.
He says: "When I was on Omagh Council I was a pariah – they wouldn't even shake hands with me... we were detested," he recalls.
He ridicules the UUP as "dumb", "steeped in nepotism", and with a "terrible degree of incompetence".
Yet the DUP needs to get closer to the other party to feed off its remaining support and, where necessary, to co-opt it into a pan-unionist alliance at election time.
Up to a quarter of DUP members are former UUP. And 27.6% of DUP members used to vote for the UUP, so the path from one party to other is well trodden.
The attitude to the TUV is more hostile. When asked which of a range of parties they would give second preference votes to, more than half (50.4%) said there was "no chance" of it being the TUV.
The UUP is by far the most popular choice, with 71.8% saying they were likely to do so and only 8.8% saying there was no chance.
In some ways the DUP and UUP complement each other; the smaller party is stronger in the west of the province. It still has a larger membership overall than the DUP.
Dealing with the UUP is seen as a tactical manoeuvre. Hostility to the TUV is visceral.
"I didn't think it (the TUV) would be a serious threat, more because the individuals that formed the TUV were people that we were quite happy to get rid of," says Paul Givan, an MLA.
"Also, as far as I am concerned, we have the evangelical fundamentalist base still with us."
That is the language of war to the knife. Also, DUP leader Peter Robinson calls for transfers to the UUP, but not the TUV.
He tells Dr Tonge: "None of us ever believed that the TUV would surpass the DUP. We knew they had the ability to damage us and maybe damage us to an extent that would allow the Ulster Unionist Party to come back into some credible position."