The primary reason it is accretive is because they are paying...

The primary reason it is accretive is because they are paying ~50% of the purchase price in low-cost debt. Nearly every NPAT generating business is an accretive acquisition under a funding structure like that (because the funding cost is <6% versus an NPAT yield well above this).

The structure of the offer makes it unlikely they will increase their offer, in my opinion. They haven't asked the SPO board for due diligence, they have simply gone straight to shareholders. Lodging a bidder's statement concurrent with the first approach, and doing a non-reversible capital raising to fund the deal, are two hallmarks of a takeover offer where engagement with the target is not seen as necessary.

On the flipside - the risk of the deal not going ahead is quite low, so if you do hold out for a bump (which is unlikely) you are taking some but not a lot of risk, I think.