Symfony2 OOP design - symfony

Question

I'm facing a OOP design problem ... My goal is to build a Improvement system.
It is really simple to understand, here is the code sample :
<?php
interface Improvement {
public function getGains();
public function isActivated();
}
// tagged "improvement"
class AImprovement implements Improvement {
public function getGains() {
return 1;
}
public function isActivated() {
return true;
}
}
// tagged "improvement"
class BImprovement implements Improvement {
private $statsCenter;
public function __construct(StatsCenter $statsCenter) {
$this->statsCenter = $statsCenter;
}
public function getGains() {
return 10;
}
public function isActivated() {
return $statsCenter->getStats()['totalGains'] > 10;
}
}
class ImprovementCenter {
private $improvements;
public function addImprovement(Improvement $improvement) {
$this->improvements[] = $improvement;
}
public funtion getGainsSum() {
$s = 0;
foreach ($this->improvements as $improvement) {
$s += $improvement->getGains();
}
return $s;
}
}
class StatsCenter {
private $improvementCenter;
public function __construct(ImprovementCenter $improvementCenter) {
$this->improvementCenter = $improvementCenter;
}
public function getStats() {
return [
'totalGains' => Money::toEUR($this->improvementCenter->getGainsSum())
];
}
}
We can create x implementations of Improvement interface. If we tag them with "improvement" they will be added to the definition of ImprovementCenter with addMethodCall by calling addImprovement.
So, ImprovementCenter has a clear dependency on all the "improvement" tagged services.
And for some reason BImprovement is enabled only if the gains in euros > 10. ( Don't ask me why ).
But we can clearly see a circular dependency : BImprovement -> StatsCenter -> ImprovementCenter -> BImprovement ...
Any ideas on how to solve it ? (I already found some solution but I need more ideas). The side goal is also to benefits lazy services loading of symfony2, ImprovementCenter must be created only if it is injected somewhere.
Thank you !
EDIT :
Here is one dirty solution that I found. First the main problem is that here I have an observer pattern with Improvements as Observers. The consequence is that ImprovementCenter (the subject) depends on all its observers, that is not the pattern goal.
Then I moved the dependencies: I have kind of an ObserverManager that depends on ImprovementCenter and all Improvents, the ObserverManager manually do $improvementCenter->addImprovement($improvement).
Now the $improvementCenter has no dependency on Improvements.
The problem is that I must initialise ObserverManager on each kernelRequest, without that trick the ImprovementCenter will not have any Improvements linked as observers.
This solution perfectly works, but it smells kind of bad .. ahah
Ideas ?