My experience belies the need to keep tweeters at ear level, I suspect it's dependent on the dispersion pattern of the tweeter, room characteristics, and personal preference. My Tidal Piano Ceras have Accuton ceramic drivers and the tweeters are positioned about six inches above ear level with no deleterious effects. If anything, I think the speaker balance with the tweeter slightly above ear level is more pleasant than being at ear level.
Those sheets of strand board your speakers are sitting on can't be doing your speakers any good though. Get something with a bit of mass for them to couple to, concrete patio pavers, granite, slate, maple. I needed something flat and solid for the feet of my speakers to sit on, they're rather like Cerapuc footers in function. Carpet definitely doesn't work with them. I got polished 20" square 50 lb. slabs of granite cut at a stone dealer for a hundred bucks, works great and definitely improved the sound compared to the lighter weight tiles I had been using.