I don't think Spire SS calculations were ever disclosed (not that I know at least) - we know that there are some non-trivial calculations in there, including AW levels. Having said that, looking at the SS numbers I assume that this is for chapter 4-5, correct? Well, that's a period in chapter progress where fighting sucks in general. You troops are weak, and you have very limited capability to replenish them quickly. This is irrespective of the Spire, which only makes things worse. There is not much you can do about that except rush forward where you will get troop upgrades and faster production.
On the other hand, if you insist on playing Spire at this stage, you may want to do more negotiation. It is relatively cheap that that point in time. I did complete the full Spire once with chapter 4 city doing pure negotiation, and with couple of diamond drops for boss fights (which was covered by the diamonds won from the Spire itself). Not something I would do on a weekly basis, but negotiating 1-1.5 Spire levels every week is certainly doable without draining the troops.