I think there are a number of unsaid rules about the P/E multiple a business should command and there is definitely no exact science that I'm aware of. For companies showing good growth like Avanti Feeds, I think markets are always trying to determine the correct P/E. But I believe there are 2 main factors which will help in arriving at some sort of a P/E range
1. Type of business - Commodity linked businesses command much lesser P/E multiples than FMCG due to predictability of earnings
2. Pace of earnings growth
For Avanti, pace of earnings growth is there for everyone to see. For type of business - you should probably go through this thread as it has evolved over the past few years.
Just to share my investment philosophy - I don't buy a business (partially) expecting P/E expansion from let's say 15 to 30, or even 6-8 to 12-13 times. That is just a MoS for me but it's not factored in my potential investment returns.