I did a little search on squish band angles and found an interesting comment on a site dealing with rc boat-racing:

Squish Band Posted Thursday, March 8, 2001 by MartenDavis
In all the testing that I have done with the dyno, backed up with a huge amount of on water testing, I have arrived at a conclusion about the configuration of the squish band. To make maximum power, make the squish band FLAT. You will get some shake (like engine being out of balance with the flat squish band). Many engines come with 3 degree across the squish band. I believe that you are giving up a lot of low end power that way (launchability). A good compromise is to make the outer 1/2 of the squish band flat and the inner 1/2 with a 1/2 degree angle. These results are using the currently available pipes for the various engines (Irwin for the 21, Big Belly CMB for the 67) All other pipes that I have tried have also produced the same characteriestics, but with a very well optimized pipe there may be some change in this result.

And:

One of the most important items in the design of a good combustion chamber is the squish band. I believe that a flat squish band produces much more power than an angled squish band. The flat squish band head has a flat area (squish band) around the perimeter of the head which comes in close proximity to the piston at top dead center. This squish band is designed to keep the layer of combustion mist very thin, in order to let heat travel quickly from a hot piston to a cooler combustion chamber (head). The thinner this layer (the closer the head clearance), the better this heat transfer is accomplished. If your head has its squish band to far away from the piston at TDC and the compression ratio is high, you will get pre-detonation (knock). You can tell if this is happening by looking at the squish band. If it looks like it has been lightly sand blasted, it is pre-detonating.


I also found another interesting post:

I currently believe the reason the little engines can stand more nitro and higher compression ratios is far more basic. That is, they have a higher surface area to volume ratio in the cylinder. Assuming:
.21: bore = 16.4mm, stroke = 16.4mm, surface area halfway along the stroke = 845 mm^2, volume = 1730 mm^3, surface area / volume ratio = 0.488 /mm.
.91: bore = 27.05mm, stroke = 24.5mm, surface area halfway along stroke = 2190 mm^2, volume = 7040 mm^3, surface area / volume ratio = 0.311 /mm.

The .21 has almost 60% more surface area per volume. This means it dissipates more heat to the cylinder walls, head, and piston per joule of heat introduced from the combustion. Therefore, for the same % nitro, compression ratio, air/fuel mixture ratio, and charging efficiency, peak flame temperatures will be lower, and detonation will be abated. So, you can run the .21s with higher c.r. and higher nitro and still lean the needle down for good power before blowing the plug.

This would explain why larger diesel engines could get hot / overheat easier than the more common small engines.