spacer notes

[chip]

I don't fully understand the issues that spacer notes cause, below are a 
couple examples.

This example of 3 measures of music with a glissando in the middle of 
them, I think the two notes with the glissando are too close together to 
print a decent looking zigzag glissando -

d b-. b b-. b b c d
e4\glissando c r8 e d c-.
b b-. b c-. a a-. a b

So I want to add a little space between those two notes, thereby making 
the glissando a bit longer and better looking. I tried the code below 
but it just pushes the last 3 eighth notes into the next measure (why?) 
causing major problems -

d b-. b b-. b b c d
<<e4 {s4\glissando s4} >> c r8 e d c-.
b b-. b c-. a a-. a b

Yet a similar bit of code works just fine for a decrescendo -

   r2 b4 b8 as
   << a2. { s4\> s4 s4\! } >> r4
   r4 c8[ d] e4 c


I've read the sections in the LM and the NR but they don't get this 
specific. Can someone help me make that zigzag glissando a bit longer?
Thanks,
Chip