Learning and tweaking the technique should not start at greater than 80% effort, and doing 250 repetitions in one session/day into a blanket doesn't ring as a very disciplined attempt to fix technique. Just two of your swings has prompted a bunch of discussion on what needs to be fixed. What do you think the other 248 did for you?
I wish I could go out and throw for distance and measure to see if my hard work is paying off. Will have to wait til spring as its just too cold here now.
I throw a lot in the garage but not just haphazardly. I usually break it down into several sessions with different discs and try to analyze how each shot felt- what did feel good and what I think needs improvement. I'm also able to see how the disc hits the sleeping bag that's hanging and adjust for angle and work on control. Very few of the shots are flat out give it absolutely everything I've got type of shots. Just from the sound and impact of the discs hitting the bag I can tell my velocity has improved quite a bit already since I first started. I've logged in about 1,300 throws now.