The answer is due to the time until expiry.That time has value...

The answer is due to the time until expiry.
That time has value that can be factored into valuation along with other parameters.
The relative prices are moving around a bit on low volumes lately making it a little tricky to say if the price is right or not at any given moment.
Technically options should be trading as close as 8 or 9c under the shares.
But they rarely get that close as a) a bit of short-term risk factored in that the shares may drop and b) the market doesn't quite seem able to factor in such a long time premium.
Even when SXP was going gang-busters in June/July the options were never fully valued based on options pricing models.

What I expect to see once SXP gets going again over coming months and years is that the options will hold around current premium levels for some time rather than seeing the time premium 'erode' in line with the actual time. Until say around two years to go when most will be able to get their heads the discount relative to time.

Eg: If you said that there was currently a 12.5c 'premium' (12.5c options v 25c shares) then that is actually the correct pricing for 700 days to go whereas we are currently at 1546 days to go.