Reasons for the firm wall:
TO discourage buying.
Entice penny flippers to sell and take profit.
Holders to sell thinking there is a big seller so holders sell and think they will be able to buy in lower.
MMs watch for bid strength, if there is light bidding, MMs take down the PPS and short the bidder and entice selling. Depending on how hard the MM try to take down the PPS, may trigger stop losses.
Some firm walls may even be real, however, yesterday, I believe there was a buyer or accum by MM.
THere are other reason, other may want to jump in.
IMO
