You're misreading the chart. It doesn't illustrate total levels of 5ar, but rather the inhibition rate. Finasteride greatly inhibits 5ar-2, and slightly inhibits 5ar-1.
I think you're fundamentally misunderstanding how this works. You say your goal is to reduce circulating dht by 90%+ rather than only 70%. However, 5-ar type 2 is responsible for roughly 70% of dht, whereas 5-ar type 1 is responsible for the remaining 30%. Therefore, to get to that level of reduction, you'd need to inhibit 5-ar type 1 in addition to type 2. There's no way around this. You may be able to achieve this by taking enormous doses of finasteride, but the benefit would come from the fact that finasteride also inhibits type 1 at such high dosages. So you might as well be taking dutasteride at that point.
To summarize, even if you were to inhibit every single 5-ar type 2 enzyme in your body, you'd still have 30% of your dht left. Any further reduction beyond that point must be the result of inhibiting type 1. Ingesting/injecting high doses of finasteride would allow you to come as close as possible to the 70% ceiling, but at that point it's probably affecting type 1 too.
Finally, while Cialis does nothing for your libido, it helps you get/maintain erections. So I suppose it could help mitigate the effects/symptoms, but not the underlying problem.