As has no doubt been pointed out, the A3 plug is a hotter plug than the OS8. This is by OS's specification. Trouble with this is that there is no industry standard for heat range measurement. One company's "Hot" might be "medium" by another's way of thinking.

Glow plugs by their very nature are sort of a black voodo witchcraft sort of thing, and nobody makes the best plug for all engines.

To this end, all you can do is while not changing ANYTHING else...try a variety of plugs and see which works best for you.

You will likely find, as have thousands of others...that the differences are far more subtle than some would have you believe.