Hi Purple Bunny,
It's pretty common for women to not orgasm from fingering. The vagina past the first inch or so does not have many nerve endings. The outer third, closest to the vaginal opening, contains nearly 90% of the nerve endings of the whole vagina, meaning the back two-thirds have 10%.
For more information on the g-spot and its location, I highly recommend this article of ours:
With Pleasure: A View of Whole Sexual Anatomy for Every Body. I do want to emphasize that if you do not feel the spongey texture, that's totally okay and normal. Everyone's body is different.
As for the particular position you're talking about, I think it might have to do with clitoral stimulation rather than the g-spot. Also, this position just gives you the chance to have some more control over things like speed and intensity, just overall pleasure.
Please let me know if any of this helps!