On the one hand we have the agenda of the investors here primarily for the Russell inclusion play. They will want to take the share price as high as realistically possible by the end of this month. The higher the market cap at that crucial data-snapshot point, the higher Insmed's free-float-adjusted weighting within the index. The higher that weighting, the greater the number of shares automatically acquired in June by the index tracker funds - and the greater the rise in share price due to the demand for millions of shares.
On the other hand it seems likely there are big investors who want to keep the share price as low as possible for as long as possible, because they see the medium/long-term value of the shares. But will they be prepared to risk selling enough shares at this point to defeat the agenda of the short-term players?