Nonsoggy spinich pie with frozen spinach
With more spinach you need to wring the hell out of it, whether you start with fresh or frozen. Cook the spinach a bit so it starts to release its liquid, then squeeze it out with your hands doing small batches at a time. When you're done with that, put it in a clean tea towel, wrap it up and twist and wring. You'll get even more liquid. I'm surprised actually that you say that you didn't wring the spinach originally but didn't have a problem with sogginess. Spinach contains a boatload of water.

{edit upon further reflection}

I would even go further than wringing the spinach. To protect against sogginess, I would briefly sauté the spinach after wringing it. That would be a great opportunity to incorporate other complementary stuff like onions or garlic too.