I would ask the LBS and fitter to not cut the steerer tube to a "final" length until you have ridden the bike for a while. In my estimation, it's better to leave an inch or more of steerer and fill the top with spacers so that you have the flexibility to move the stem up or down if you find things aren't quite right. It saves having to fiddle about with stem angles.

Personally, I've not used a fitter except for our Santana tandem (that was part of the purchase deal, and the fit was no different to what I would have come to). But with the back issues and age of the OP, a full fit might be worth the cost.

And I will join others in saying that the slope of the top tube in compact frames is irrelevant to the geometry of the rest of the bike except for standover height.