Possible institutional buyer tactics, given the obligation to acquire TSLA prior to December 21st:
1) get it over with early, so that if the price is higher, your fund benefits from that
2) leave it until the last few days, or even until the last minute, either because you're selling other assets to generate liquidity, or you think you will get a great deal at the end, or you just don't want to buy TSLA... or whatever other reason
3) more or less just buy at a constant rate. no point getting worked up one way or the other. Unlikely everyone starts on the same day though, as they needed to "confer" and draw up tactics.
The institutional buying is occurring with some proportion of those three possibilities... right? I can't see the SP action changing between now and December 21st. Hard to believe it will do anything other than keep on climbing.
32 trading days between announcement and joining the index. 6 days into that TSLA has climbed an average of $24.55/day. Does that mean it will continue and end up at $1,193.64 by close on Dec 21st?
Or if calculated as a constant fractional appreciation... 6 days into that TSLA has climbed an average of 5.27%/day. Does that mean it will continue and end up at $2,111.08 by close on Dec 21st?
Third possibility: the percentage of climb changes upwards towards the end, as available shares start to dry up (shorts covering, less and less stockholders selling, etc.)