When I've made a 100% rye in the past I've never had much oven spring. The cracks come from topping the dough with flour (or seeds in your case) which then come apart as it rises so you should see almost the finished pattern before it goes into the oven.
When I've made a 100% rye in the past I've never had much oven spring. The cracks come from topping the dough with flour (or seeds in your case) which then come apart as it rises so you should see almost the finished pattern before it goes into the oven.