I see this signature too complicated and a lot of rules, already menberi rewards too small but made complicated way, receive a payment every month again, .. 
It is the standard rule of almost all sign campaigns and the rate is fair enough if you have a good math to count the rate.
Look at this :
Hero Member : 0.1 per month for 90posts = 0.0011xx per post
Sr. Member : 0.075/month = 0.00083 per post
Full Member : 0.05/month = 0.0005xx per post
Member : 0.025/month = 0.00027xx per post
And now please take a look at other campaigns, there are some other campaign have lower rate than this one. Anyway, you are newbie then why you complaining for something that you cant even participate on it?
The rate per post is not mentioned as the OP mentions minimum number of posts required as 90. Maximum number of posts per month is not mentioned.
Why you should care about the maximum post allowed for a fixed rate campaign? No matter how many posts you made you wont get any additional payment because it is clear that you only need 90 qualified posts/month to be eligible for payment.
Logically, why you need to make more than let say 120posts for 0.1 while you can get the same amount for 90posts only. Maximum posts should be only occurs on pay per post campaign instead of fixed rate campaign.