There is no reason that one will pay the same amount to get insurance for a 20K player like a 2M player.
Maybe they can put a percentage to the wage? Like 0% insurance, 20% insurance, 40% insurance. Because he has a point there though. Teams who hire good doctors would be paying insurance and hardly getting anything back.
aybe the insurance can be affected by doctors level, like real insurance predict the risk whle making an contract. But you should also consider that they like to earn money to, so you normally pay more then you get back and with the small sums of the salary i think gambling won't be so effective them.
And yes like it was said from Pini, it should depend on the value/salary of the player, since it would be ridicoulus if a 400k center would cost the same like a 5k center.