Hi Corey, I seem to remember that you are already using the Slicing Pie method
for your equity. In my experience there is no good scientific model for seed stage/angel investing which is why I promote the use of dynamic splits.
I call the seed-stage valuation the "magic number." It's large enough to be good for you and small enough to be good for investors. If you are concept stage you are selling the dream and you may actually get more if you have a good track record. I once raised $5 million with nothing more than a PPT deck. I had some good experience and my partner had some good success.
If you have a little bit of track record that will be a determining, often limiting, factor. I often see startups who wait to raise money until after they launch their product only to find that investors want to wait and see how it does.
For most tech startups I tell founders to start at about a $1,000,000 pre money and go from there. No science, just experience.