Foxing it wrong

For quite some time I've asked questions about bending the waist part of
the sides in a Fox bender.  I've never really got much on it.  Someone
said the slats were plenty hot ehough.

I've read every web site that has anything about it.  One site said run
the screw down slowly.  Nothing else I could find on this specific
issue.

It seems my concerns were well founded.  I built my first bender.  I put
the slats in and heated it up - longer than anyone has said to do it. 
The slats conformed to the mold shape somwhat.  I put the sides in and
started the screw down.

Exactly as I had expected, the bottom slat didn't even touch the side
material - so it didn't get hot enough from the top slat only.  And,
therefore it cracked at the waist.

So what in tarnation am I missing?

I tried a work around with a bit of success.  I put objects of various
thicknesses under the waist and screwed it down far enough to make both
slats contact.  Then I ran the screw up, put the next thinner object in
place of the first etc.

This met with limited success, as both slats were cooling all this time. 
Altho using a length of 2" pipe as the shoe gave me a heat reserve on
the top side of the side.  But the top isn't what's breaking out.  But I
finally got what I was after some time.

Someone used the term "magical" to describe using the Fox or variations
thereof.  I'd say the same for the bouts, but the waist is a problem
here.

So are you guys taking half an hour running the screw down?  If so,
what's going on with the bouts during that time?  Obviously you can't
run the bouts down very far without the waist down at least most of the
way.

It occurs to me that I might put in a piece of metal that could be
raised up against the bottom slat and pressing it against the wood
before the screw starts down.  Does anyone do that?

Jim L