alternative to poke test for multigrain sandwich loaf

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sometimes I hit it right with the poke test on a multigrain sandwich loaf, but most times the result is under proofed.

The finished loaf splits about 20 mins into bake around the top of the loaf.

The crumb and taste are what I'm looking for other than the split. 

It's definitely hydrated enough at 65% or more.

It's made with 2c of 100% starter and the starter is quite active when I add & mix the dough.

~800g flours including whats in the starter and added to it.

Taking about 45m to double in size off 30g each flour and water added to the starter.

Is there another method to check for proper rise time or just have to add time each time till I get there.?