[Therion] -size -r-size and -l-size on line label

[Andrew Atkinson]

On page 68 of the Therion book

Customizing text labels
There is a preliminary interface to changing font sizes for labels via 
the METAPOST
macro
fonts_setup(<tinysize>,<smallsize>,<normalsize>,<largesize>,<hugesize>);
which may be used inside of the code metapost section of the layout 
command. <normalsize>
applies to point label, <smallsize> applies to remark and all other 
point labels.
Each of them may apply to line label according to its -size option.
Example:
code metapost
fonts_setup(6,8,10,14,20);
% default values depend on scale; for 1:200 they are 7,8,10,12,14

Now this works well when I have used -scale m etc on the line label. But 
as I changes text sizes it sometimes overlaps the passage, as it seems 
to use the line as a centre. so I wanted to try something cleverer, 
similar to the -align available with point label, align only works with 
points

and on page 26 it gives me this

size <number> ◃ line width (left and right sizes are set to one half of 
this value)
r-size <number> ◃ size of the line to the right
l-size <number> ◃ same to the left. Required for slope type.

Which suggests to me, with page68, that I should be able to use

-r-size normalsize

which would  put the text on the right side only

but got the error

no line point specified
(tried adding -l-size 0 just in case this was needed, but same error)

Also checked by adding a number as well eg

-r-size 20

but same error.

Am I trying to misuse this option? If not what am I missing?



If I have not interpreted this right, is there a way to make the text 
only be on the left or right of the line


thanks

Andrew