Gary Sensei pointed out - after meeting the strike and projecting uke’s arm toward his head, hold that arm up, while shikko in behind uke.   I was meeting the strike and letting uke’s arm down while i shikko in behind.   That leaves me with uke’s arm in front of me and no momentum.   This leads to dragging uke down with arm force.  By keeping the arm up, i keep uke off balance while i enter and then use the momentum of the falling arm with centrifugal force to bring uke into Ikkyo pin.

Another good point – keep projected arms in front.   I think i am trying to get 180 degrees around, leaving my arms off to the side.   So my tenkan should leave me projecting into uke’s center with my arms in front.