OK it looks like the font rescaling is not always as straight forward as I thought, but I found a very simple way to reduce the minimum line spacing (while still leaving it adjustable via the line spacing slider) that works for the books I have tried which have font sizes set in terms of "font-size:small", "font-size:medum:", etc., the main text being set to font-size:medium):
All I did was remove any occurrence of "line-height" from the CSS stylesheet, then added the following line to the top of the stylesheet:
Code:
body {font-size:80%}
Now I can adjust the line spacing down to the point of being almost unreadibly close on the minimum setting (line height 1.3*0.8 = 1.04 I think), and with the slider on the 4th notch from the left the line spacing is about the same as the prevoius minimum (line height 1.6*0.8 = 1.28, close to the original minimum of 1.3).
(The left-most slider notches set readingLineHeight to 1.3, 1.35, 1.4, 1.6, ..., etc. It seems that if I set the body font-size to 80% then the line spacing for fonts of size medium becomes 0.8*1.3, 0.8*1.35, 0.8*1.4, 0.8*1.6, ..., etc.)