In response to this problem, I had something in mind for many years. Due to the existential sloth that keeps so many of us living lives of quiet desperation, I never acted on it. But I offer it for your consideration.
You need a fishing partner with the same mindset and interest in hooking steelhead that you have. (It will save some money if you're both the same size.) You both need basic swimming skills. You'll need one to share, or two neoprene diver's suits, and a scuba mask, and a weight belt.
See where this is going? In likely steelhead holding places, you take turns hanging out under water, observing, and perhaps filming with a GoPro, while the other fishes with an assortment of lines, sinktips, leaders, and flies of assorted densities. Coach each other as to where to cast, how much to mend, whether and when to pulse, retrieve, skitter. Share everything that you see and experience.
If you do your testing in empty water, you'll learn a lot about what it takes to position your flies at the level where you think that steelhead would be. But if you do it in water that holds steelhead, you'll learn too how the steelhead react to your lines and flies. Will they ignore them, flinch, drift elsewhere, nip or make short pursuits? That would be diamonds on top of gold.
The cost won't be much compared with the steelhead fly tackle you already have. If you think that the time you spend under water observing is wasted, you aren't remembering the frustration of countless hours of fishing for all you're worth and not catching a steelhead, or learning diddly about why you're not catching.
And if you film it, next year, you and your buddy may be on the fly fishing film circuit!