How do improve oven-spring

Hi All -

I wonder whether there is someone on this forum able to comment on (probably) my last concern.

After a long time of trying, I have finally come to the point where the loaves are acceptable to almost all who have tasted them: a 70%rye-30%wheat flour Mischbrot (70%hydration); with a 6% mixture of a soaker of bulgar wheat, wheat germ, barley or oats, bread spices loosely based on German Brotgewuerz, and prepared using the Detmold 3-stage process.

The only thing that is missing is a decent oven-spring. I know that oven-spring is difficult with these high proportions of rye flour, but I have had better oven-spring in the past. Then I wasn't using the Detmolder 3-stage process, which certainly gives a better tasting rye bread and I would like to stick with it.

The latest loaf is only about five and a half cm high, whereas previous ones reached nearly always about seven to eight or even more, all always done in a one-kg Banneton.  

I feel it can be done ... suggestions of how to achieve this are greatly appreciated,

Eberhard