It appears that I can only enter whole numbers for tempo changes in play mode. As a result I often cannot align hitpoints to a beat or bar. I know you can create fractional bpm markings using engrave mode tempo options but these do not show up in play mode, only in the score.
Is there any method I am missing to increase the accuracy of hitpoint alignment to the grid using fractional tempos?
No, I don’t think so, unfortunately. But any tempo that appears in Write mode will appear in the Time track in Play mode, and vice versa; you may have hidden the signposts for hidden tempo items in the View > Signposts menu, perhaps?
I confirm that fractional bpm changes in write mode do show up in play mode. The problem is that it is not very user friendly to have to tweak in write mode to have the hitpoint show correctly in play mode (when dealing with fractional values). Any adjustments in play mode are only integers and this will then reflect back into write mode. It looks like I’ll have to make the tempo map outside of Dorico and import it in. Hopefully there will be an update in the future.