Natural coals question

[E.G.]

I've been using lemonwood coals, and I do like them a lot. 
Neutral flavor, good burnign time, nice temperature.  But I've
noticed lately that it seems that after smoking with them for a bit (10
minutes or so) the heat seems to die off. 

When I pick up the coal to tap the ash off, the bottom of the coal is
all black -- it doesn't appear to be burning!  The rest of the
coal is nice and hot, but for some reason the bit of the coal in
contact with the foil seems to be getting extinguished.

Any ideas why this might be happening?  I do make sure they're
good and red all over on the stove before I start using them. 
Could it be I need more holes in the foil under the coals?

E.G.

[Mathazar]

I certainly hope that isn't going to happen to me,  because I just
placed an order yesterday for 15 (500g) bags of Romman Lemon Wood
Coals 

[cypress]

I have no prolem with my lemonwood. They work better for me when they
are in smaller chunks. The heat disperses better and the coals breath
better.

[MR Bubble]

How long of a time are you taking between puffs?
MR Bubble

[E.G.]

Maybe 30 seconds to a minute or so, and two puffs at a time.

E.G.

[NERV]

are you making sure they are 100% red hot b4 u use them? my local
hookah louge seems to place their coals so they arent flat on the foil,
seems if they arent touching as much they last longer