Singapore Airlines (SIA) has lifted its stake in Tigerair to about 74.5 per cent but there are signs some investors are holding out in hope of a better offer.

SIA is still some way off the 90 per cent it needs to take the budget carrier private, which may be behind its move to extend the deadline for the $453 million takeover bid. The offer's original cut-off date was Monday but SIA has pushed back the closing date to 5.30pm on Jan 8.

SIA held 55.73 per cent of Tigerair when it announced its takeover bid of 41 cents a share on Nov 6.

It has garnered "valid acceptances" of an additional 18.76 per cent, or about 469 million shares, as at 5pm on Monday, according to a stock exchange filing yesterday.

This gave SIA and its concert parties 74.5 per cent of Tigerair, or about 1.86 billion shares.

SIA's takeover is conditional on it owning more than 90 per cent by the close of the offer. It aims to delist the carrier and fully integrate it within the SIA group.

SIA is offering 41 cents a share in cash - 32.3 per cent higher than Tigerair's closing price of 31 cents on Nov 5. Tigerair shareholders can also opt to subscribe for SIA shares at $11.1043 each. But these options are not compelling enough for some investors who hope SIA might lift its offer to "upwards of 50 cents".

Mr John Teo, who holds 30,000 to 50,000 Tigerair shares, said: "Tigerair is quite valuable to SIA and that's why it is keen on the takeover. But it should be able to offer more than 41 cents. Previously, it bought shares from Temasek at a much higher price."

SIA bought Temasek Holdings' 7 per cent Tigerair stake in 2013 at 67.8 cents a share. It also purchased perpetual convertible securities that were eventually converted to shares at 56.5 cents apiece last year.

Veteran investor Mano Sabnani, who owns 20,000 Tigerair shares, also felt that SIA should consider improving its offer: "At this stage it is like a half measure if you offer 41 cents and you just back off."

Market watchers were not surprised that SIA failed to reach the required 90 per cent threshold when the original deadline rolled by, said NRA Capital research director Liu Jinshu, as there were "mixed opinions" over the offer price.

However, Mr Liu noted that investors could exchange Tigerair shares for SIA shares, which rose seven cents to $11.19 yesterday.

"They can convert them to SIA shares at about $11.10 per share, which is lower than (Tuesday's) price. So there is an additional premium built into the offer price, given the options," noted Mr Liu.

But some investors told The Straits Times that they are not keen on that option either. "The SIA share offer is not attractive at all," said stock broker Adrian Ho, who holds 120,000 Tigerair shares.

"SIA shares have dipped below the benchmarked price for the exchange since (the offer) was announced. I'd rather take cash."

Investors said there is a slight concern that Tigerair shares may weaken if the takeover bid fails but the long-term prospects seem better.

Mr Ho said: "SIA probably has greater plans for Tiger, so maybe down the road there may be a better offer. Or maybe it will try to merge Scoot with Tiger."

Investors feel SIA will back Tigerair, given its major shareholding in the carrier. Tigerair shares closed unchanged at 40.5 cents yesterday.