Ajayi’s return to his best form has coincided with the Millers embarking on a six-match unbeaten run and climbing to seventh place in the League One table.
Yet Warne now wants the defender, who fell out of favour after some costly early-season gaffes before earning a recall, to be a bigger threat at the other end of the pitch.
“I think he’s been really good,” said the boss who has been nominated for the Sky Bet League One December Manager of the Month award.
“I’m pleased with Semi above anyone really. His performances have come on leaps and bounds.”
Ajayi took his goal tally to three with a first-minute strike in the 2-1 win at Walsall on December 30.
“It’s nice for him to score,” Warne said. “In the great teams I played in, if your centre-halves can get eight goals a season, the pair of them, then you’re laughing. It takes the pressure of the strikers.
“Every time there is a set-piece at the moment, I fancy Semi to score.”
With Ajayi hitting the standards he set in the Championship last term and versatile Will Vaulks also showing up well as a centre-half, Rotherham’s need for a new central defender in the January transfer window has lessened.
Warne wants to add some height and physicality up front following the departure of prolific loan striker Kieffer Moore and the Millers are hot on the trail of a new frontman.
Warne’s men head to Oldham Athletic on Saturday looking to break into the play-off reckoning and could be boosted by the return of winger Jon Taylor after a two-month injury absence.
Taylor has been out since November 11 but was back training before Rotherham had a rare weekend off last week and may make the squad for the Latics clash.
Captain Lee Frecklington, a transfer target for home-town club Lincoln City, has been receiving treatment for a calf complaint which forced him out of the Walsall match in the second half. Fellow midfield man Darren Potter is unlikely to be ready as he recovers from an achilles problem.
Winger Anthony Forde, another player to impress in recent weeks, believes Rotherham are capable of being in the promotion mix this year.
“We’re only just over halfway through the season,” he said. “I wouldn’t rule out anything. We have to keep our heads down and focus on each game. We have momentum now.”
The Manager of the Month winner will be announced on Friday. Warne faces competition from Derek Adams (Plymouth Argyle), Paul Hurst (Shrewsbury Town) and Kenny Jackett (Portsmouth).
The Millers have received a further 400 tickets for the Oldham trip after selling out their initial 547 allocation.