@AAvi , not an expert but will share my understanding.
Typically, for genuine SME IPOs, 3-7% of the IPO size can be considered reasonable for spending on the IPO process. Anything over that, generally, indicates that the company has paid extra just to get the issue some extra mileage and push. With these additional funds, GMPs are pumped and several fake orders are put during the the pre-open to entice gullible investors, only to withdraw such orders just before 9.45. (Same trends were seen this morning too.) If retail investors do get enticed to jump in at the time of pre-open the opening price remains high, and the "settlors" exit swiftly, thereby causing the price to inuously thereafter. Other recent examples - Finelistings, Deem Roll Tech.
Re: Underwriting..more it is being underwritten by the LM, better is the confidence shown.
This is just my limited view and understanding, please do not take this as the holy grail.