What you gain in the scrum power of Mike Ross, you lose in the lineout lifting technique of John Hayes. That is the specific difference in the improvement of the Ireland scrum and the ongoing problems at the lineout.
The overall responsibility for the set-piece play rests on the ample shoulders of forwards coach Gert Smal. He did not fudge the issue out in Killiney Castle yesterday.
"I am not satisfied in the first place," he said.
"I won't be satisfied until we get 95% plus success rate. We are continuously working on all aspects of lineout play. When you select sides, you look at a couple of factors.
"The lineout is not the only part of the game. There are a lot of players. I can select the best lineout forwards in Ireland. But you have to ask the question: are they going to give you what you want?"
In the recent past, Ireland was viewed as a lineout orientated pack for the implementation of their driving maul and for looking to strike from first phase. It was the reason Hayes was trusted for so long.
The new rules have put a greater emphasis on the scrum where referees have been keen to penalise because of the interminable delays in the new call system there.
"You look at defence. You look at lineouts. You look at scrummaging. You look at a lot of factors. It is not just isolated things that you look at. We will keep on working on it," said Smal.
There is light at the end of the tunnel. Rory Best is a relatively clean thrower. Paul O'Connell is still one of the best lineout exponents in the world. Donncha O'Callaghan is secure at number two.
Despite a lack of inches in the back row, Sean O'Brien, David Wallace and Jamie Heaslip are all sound handlers of the ball and they have been used to win possession out of touch.
On the other side of the coin, the cornerstone tight-head Mike Ross and fast-improving loose-head Cian Healy have given Ireland the sort of scrum ball to devastate defences when it is used in the correct manner.
"Getting away from Mike -- he is progressing really nicely -- Cian is still on a learning curve. It takes a couple of years to really be a strong campaigner, deal with all the different tactics the opposition throws at you," said Smal.
Healy has been able to handle monster challenges, like Italy's Martin Castrogiovanni and France's Nicolas Mas. He has been cornered into a stiff apprenticeship.
The Irish scrum is not wilting. There were problems against Italy. There was significant progress against France. Scotland were crumbled, admittedly without Euan Murray.
Is Healy an international-class scrummager now? "He is playing well. He might struggle with one or two things. But, Greg (Feek, scrum coach) is always close by to pick up on things," Smal stated.
The Irish scrum and lineout will be tested in Wales where British and Irish Lions tight-head Adam Jones will surely return from injury and Alun Wyn-Jones will have his jumpers primed.