[Groff] groff and papir size again

[Mike Iokhvin]

Hello All!

I have groff 1.17.2, and I try to make a book with groff -me. Unfortunaly, 
the book-size is not standart (it's 20cm x 13.5cm). And I make this book on 
A4-papir with many blank space on the corners. 

I Use:

.po 5.49515c 
to offset from left corner of papir

.pl 25 c
to make total lenght of papir 25 cm

.m1 5 cm 
to make ofset from top of papir to text

.m3 0.6c
to make offset from bottom footer to text in 0.6 cm

This is work, but on some page I have strange offsets from footer to bottom 
part of text. On some pages All is Ok -- I have exectly 0.6 cm, but on some 
pages I have 0.6 cm + height of one string. It's look no good. What can I 
do? And where is my mistake (why groff leave one empty string on some 
pages)?

-- 
Best regards,
        Tashi Tsering