mIRC uses font linking, which is probably what you are noticing with different sizes on the same line. If you use a font that does not support a given character, then mIRC will find a font on your system that does support it and display the character using that font. mIRC attempts to keep the character size close when doing this, but fonts don't all have the same sizes and sometimes you run into a situation where something like size 10 is too small and size 11 is too big because the font doesn't have a size that matches the original font. If you use a unicode font, you will not notice this very often (if at all) because the font should support all characters you are using. There may even be a new Lucida font that includes unicode characters. Looking at Lucida Console in charmap shows that it does not include the character ಠ, so this is most likely the problem you are facing.
Note that I don't know too much about font linking in terms of font sizes, so I may be incorrect in what is above, but I am pretty certain it is accurate.
