About the dropcaps, I could not get it to work either. I changed the eighth value in the font size rescaling key to 60 and the size of the dropcap letter grew larger, but the size of the space beneath it also grew. And this with line spacing and line height set to zero. I've also fooled around with the epub and changed the value of the line height there, but still no difference. I exploded the azw3 and changed the value there but still nothing.
The thing is that the changes I made would appear okay in Calibre viewer (dropcap letter size okay and space beneath it okay) but in my Kindle and in Kindle previewer, the space beneath the letter is back. I am really totally at a loss.