In reply to JohnBson:
> In my B3 boots I'm struggling to drop my heels at all without my front points coming out. When climbing mixed I can't rotate my crampons to bring my secondary points into contact with the wall below the edge.
On ice or mixed, the style of the secondary points has a big impact on this - see my little video at the bottom of this review
http://www.ukclimbing.com/gear/review.php?id=6227 but its not really necessary on mixed holds, just keep your foot still-ish! When I lived in Scotland in the 90s the fashion was for crampons for mixed not to have secondary points that protruded much because it was argued that they would push your front points of edges.
> I think the reason for this is that my boots don't grip my heel and I feel really unstable. I can climb well in my B2s on rock but my b3s seem to put a lot of force on the ball of my foot making it feel like I've got a big lever trying to work across the foot.
Can you not put your main crampons on your lighter boots? What crampons is it that you are having problems with? Like other have said, changing the fit of your boots (lacing tighter round the ankle, bigger foot beds, even thicker socks, might solve that issue - although I can't see how dropping your heels makes your front points come out...